<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilities" xlink:href="dbx-20180930.xsd#AccruedAndOtherCurrentLiabilities" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilitiesDetails" xlink:href="dbx-20180930.xsd#AccruedAndOtherCurrentLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilitiesTables" xlink:href="dbx-20180930.xsd#AccruedAndOtherCurrentLiabilitiesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestments" xlink:href="dbx-20180930.xsd#CashCashEquivalentsAndShortTermInvestments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsContractualMaturitiesOfShortTermInvestmentsDetails" xlink:href="dbx-20180930.xsd#CashCashEquivalentsAndShortTermInvestmentsContractualMaturitiesOfShortTermInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsNarrativeDetails" xlink:href="dbx-20180930.xsd#CashCashEquivalentsAndShortTermInvestmentsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsScheduleOfCashCashEquivalentsAndShortTermInvestmentsDetails" xlink:href="dbx-20180930.xsd#CashCashEquivalentsAndShortTermInvestmentsScheduleOfCashCashEquivalentsAndShortTermInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsTables" xlink:href="dbx-20180930.xsd#CashCashEquivalentsAndShortTermInvestmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CommitmentsAndContingencies" xlink:href="dbx-20180930.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:href="dbx-20180930.xsd#CommitmentsAndContingenciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CommitmentsAndContingenciesScheduleOfFutureMinimumPaymentsDetails" xlink:href="dbx-20180930.xsd#CommitmentsAndContingenciesScheduleOfFutureMinimumPaymentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CommitmentsAndContingenciesTables" xlink:href="dbx-20180930.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CondensedConsolidatedBalanceSheets" xlink:href="dbx-20180930.xsd#CondensedConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:href="dbx-20180930.xsd#CondensedConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfComprehensiveLoss" xlink:href="dbx-20180930.xsd#CondensedConsolidatedStatementsOfComprehensiveLoss" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfOperations" xlink:href="dbx-20180930.xsd#CondensedConsolidatedStatementsOfOperations" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfOperationsParenthetical" xlink:href="dbx-20180930.xsd#CondensedConsolidatedStatementsOfOperationsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPolicies" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPerformanceObligationsDetails" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPerformanceObligationsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLivesOfPropertyAndEquipmentDetails" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLivesOfPropertyAndEquipmentDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesTables" xlink:href="dbx-20180930.xsd#DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/DocumentAndEntityInformation" xlink:href="dbx-20180930.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/FairValueMeasurements" xlink:href="dbx-20180930.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/FairValueMeasurementsDetails" xlink:href="dbx-20180930.xsd#FairValueMeasurementsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/FairValueMeasurementsTables" xlink:href="dbx-20180930.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/GeographicAreas" xlink:href="dbx-20180930.xsd#GeographicAreas" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/GeographicAreasDetails" xlink:href="dbx-20180930.xsd#GeographicAreasDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/GeographicAreasTables" xlink:href="dbx-20180930.xsd#GeographicAreasTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/Goodwill" xlink:href="dbx-20180930.xsd#Goodwill" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/GoodwillDetails" xlink:href="dbx-20180930.xsd#GoodwillDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/IncomeTaxes" xlink:href="dbx-20180930.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/IncomeTaxesDetails" xlink:href="dbx-20180930.xsd#IncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/NetLossPerShare" xlink:href="dbx-20180930.xsd#NetLossPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/NetLossPerShareScheduleOfEarningsPerShareBasicAndDilutedDetails" xlink:href="dbx-20180930.xsd#NetLossPerShareScheduleOfEarningsPerShareBasicAndDilutedDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/NetLossPerShareScheduleOfPotentiallyDilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDetails" xlink:href="dbx-20180930.xsd#NetLossPerShareScheduleOfPotentiallyDilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/NetLossPerShareTables" xlink:href="dbx-20180930.xsd#NetLossPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/PropertyAndEquipmentNet" xlink:href="dbx-20180930.xsd#PropertyAndEquipmentNet" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/PropertyAndEquipmentNetNarrativeDetails" xlink:href="dbx-20180930.xsd#PropertyAndEquipmentNetNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/PropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails" xlink:href="dbx-20180930.xsd#PropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/PropertyAndEquipmentNetTables" xlink:href="dbx-20180930.xsd#PropertyAndEquipmentNetTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/RelatedPartyTransactions" xlink:href="dbx-20180930.xsd#RelatedPartyTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/RelatedPartyTransactionsDetails" xlink:href="dbx-20180930.xsd#RelatedPartyTransactionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/RevolvingCreditFacility" xlink:href="dbx-20180930.xsd#RevolvingCreditFacility" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/RevolvingCreditFacilityDetails" xlink:href="dbx-20180930.xsd#RevolvingCreditFacilityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquity" xlink:href="dbx-20180930.xsd#StockholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityCoFounderGrantsDetails" xlink:href="dbx-20180930.xsd#StockholdersEquityCoFounderGrantsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityCommonStockConvertiblePreferredStockPreferredStockDetails" xlink:href="dbx-20180930.xsd#StockholdersEquityCommonStockConvertiblePreferredStockPreferredStockDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityEquityIncentivePlansDetails" xlink:href="dbx-20180930.xsd#StockholdersEquityEquityIncentivePlansDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityScheduleOfPreTaxIntrinsicValueDetails" xlink:href="dbx-20180930.xsd#StockholdersEquityScheduleOfPreTaxIntrinsicValueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityScheduleOfStockOptionAndRestrictedStockActivityDetails" xlink:href="dbx-20180930.xsd#StockholdersEquityScheduleOfStockOptionAndRestrictedStockActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.dropbox.com/role/StockholdersEquityTables" xlink:href="dbx-20180930.xsd#StockholdersEquityTables" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilities" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilitiesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/AccruedAndOtherCurrentLiabilitiesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestments" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsContractualMaturitiesOfShortTermInvestmentsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_2396D3ABD0FCCEC888C9E1FE1E8CA46B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_2396D3ABD0FCCEC888C9E1FE1E8CA46B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_A828C339C8565E23D2F1E1FE1E8C6DD2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_2396D3ABD0FCCEC888C9E1FE1E8CA46B" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_A828C339C8565E23D2F1E1FE1E8C6DD2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_A828C339C8565E23D2F1E1FE1E8C6DD2" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_A828C339C8565E23D2F1E1FE1E8C6DD2" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashMember" xlink:label="loc_us-gaap_CashMember_37DEDBC822BC8D839841E1FE1E8C56ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F" xlink:to="loc_us-gaap_CashMember_37DEDBC822BC8D839841E1FE1E8C56ED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="loc_us-gaap_MoneyMarketFundsMember_45A6DBBAB19C6F646589E1FE1E8D7E23" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_F1BEAACA650BED65C0D9E1FE1E8C7B6F" xlink:to="loc_us-gaap_MoneyMarketFundsMember_45A6DBBAB19C6F646589E1FE1E8D7E23" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_951B6A59D0C323428256E1FE1E8DEE40" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_951B6A59D0C323428256E1FE1E8DEE40" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_91E11C2B714E4DF3AB04E1FE1E8EE3F4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_91E11C2B714E4DF3AB04E1FE1E8EE3F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditAndDebitCardReceivablesAtCarryingValue" xlink:label="loc_us-gaap_CreditAndDebitCardReceivablesAtCarryingValue_9BC0893820D2F5AFAFD1E1FE1E8E7906" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_us-gaap_CreditAndDebitCardReceivablesAtCarryingValue_9BC0893820D2F5AFAFD1E1FE1E8E7906" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions" xlink:label="loc_dbx_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_1FCB44028C275879D9F6E1FE1E8E4EA0" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_dbx_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions_1FCB44028C275879D9F6E1FE1E8E4EA0" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale" xlink:label="loc_dbx_OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale_287EC9395EF2F169F3B5E1FE1E8E279C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_2F9F7F3F22A6AB766DEAE1FE1E8D1916" xlink:to="loc_dbx_OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSale_287EC9395EF2F169F3B5E1FE1E8E279C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsScheduleOfCashCashEquivalentsAndShortTermInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_4B4063CB4696179286CFDFFBD07C0CDD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_4B4063CB4696179286CFDFFBD07C0CDD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_7D5B8EC0710A3C7C0F71DFFBD07D70CF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_4B4063CB4696179286CFDFFBD07C0CDD" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_7D5B8EC0710A3C7C0F71DFFBD07D70CF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_7D5B8EC0710A3C7C0F71DFFBD07D70CF" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_7D5B8EC0710A3C7C0F71DFFBD07D70CF" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashMember" xlink:label="loc_us-gaap_CashMember_2CBE384B1D98B3C90D40DFFBD07D180C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B" xlink:to="loc_us-gaap_CashMember_2CBE384B1D98B3C90D40DFFBD07D180C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="loc_us-gaap_MoneyMarketFundsMember_E9DC8FF5C9738C64D354DFFBD07E62B7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B" xlink:to="loc_us-gaap_MoneyMarketFundsMember_E9DC8FF5C9738C64D354DFFBD07E62B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_019A497F342E76C64E6FDFFBD07E7202" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_6C603C7E57B9583661AADFFBD07D576B" xlink:to="loc_us-gaap_CommercialPaperMember_019A497F342E76C64E6FDFFBD07E7202" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="loc_us-gaap_FinancialInstrumentAxis_A8248A5F334F71433DCDDFFBD07E4E58" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_4B4063CB4696179286CFDFFBD07C0CDD" xlink:to="loc_us-gaap_FinancialInstrumentAxis_A8248A5F334F71433DCDDFFBD07E4E58" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_A8248A5F334F71433DCDDFFBD07E4E58" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_A8248A5F334F71433DCDDFFBD07E4E58" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_D475AB429A7DD79C0A1EDFFBD07FA79B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_D475AB429A7DD79C0A1EDFFBD07FA79B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USTreasurySecuritiesMember" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_A6C147EEBE77ED67BD68DFFBD07F6F96" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_A6C147EEBE77ED67BD68DFFBD07F6F96" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="loc_us-gaap_CertificatesOfDepositMember_F00D5B9E33BC61AD6FD8DFFBD07FCED4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:to="loc_us-gaap_CertificatesOfDepositMember_F00D5B9E33BC61AD6FD8DFFBD07FCED4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_8CA7205B13E17B158FACDFFBD0801D6D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:to="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_8CA7205B13E17B158FACDFFBD0801D6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_A27F2345911583AB0FE4DFFBD080CADF" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_A583A8E276201B2BF561DFFBD07E6CEB" xlink:to="loc_us-gaap_CommercialPaperMember_A27F2345911583AB0FE4DFFBD080CADF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_64DF6860EB947C60FE2ADFFBD0801C4C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_64DF6860EB947C60FE2ADFFBD0801C4C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_2A49ECF8FE5B5B8F908CDFFBD080FFBB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_2A49ECF8FE5B5B8F908CDFFBD080FFBB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_B18A7CF29FE8606BDC13DFFBD0813759" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_B18A7CF29FE8606BDC13DFFBD0813759" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_10DE077B662B3875A96DDFFBD081D6E8" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_10DE077B662B3875A96DDFFBD081D6E8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_AF0235BE7F8C30C22049DFFBD081AF69" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_AF0235BE7F8C30C22049DFFBD081AF69" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_5F6016ED235F24A82600DFFBD082B3EF" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_5F6016ED235F24A82600DFFBD082B3EF" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost" xlink:label="loc_dbx_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost_EB50B4EDC1D12F0B2BC3DFFBD082503E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_dbx_CashCashEquivalentsAndShortTermInvestmentsAmortizedCost_EB50B4EDC1D12F0B2BC3DFFBD082503E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_C43C1672A28274C5FBF2DFFBD0828497" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_FFF704DFB0EE2C9C53BBDFFBD080BEC2" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_C43C1672A28274C5FBF2DFFBD0828497" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CashCashEquivalentsAndShortTermInvestmentsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingenciesLineItems" xlink:label="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingenciesTable" xlink:label="loc_us-gaap_LossContingenciesTable_535B9E5EE75259428FD6E000868D537A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_us-gaap_LossContingenciesTable_535B9E5EE75259428FD6E000868D537A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_A1A979FA5EA0B7FE53DDE000868E348D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_535B9E5EE75259428FD6E000868D537A" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_A1A979FA5EA0B7FE53DDE000868E348D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_333441AA4AD2737D161EE000868E4663_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_A1A979FA5EA0B7FE53DDE000868E348D" xlink:to="loc_us-gaap_LossContingencyNatureDomain_333441AA4AD2737D161EE000868E4663_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="loc_us-gaap_LossContingencyNatureDomain_333441AA4AD2737D161EE000868E4663" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_A1A979FA5EA0B7FE53DDE000868E348D" xlink:to="loc_us-gaap_LossContingencyNatureDomain_333441AA4AD2737D161EE000868E4663" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialStandbyLetterOfCreditMember" xlink:label="loc_us-gaap_FinancialStandbyLetterOfCreditMember_4BF7C5B2C7636684A63AE000868E6B4E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_333441AA4AD2737D161EE000868E4663" xlink:to="loc_us-gaap_FinancialStandbyLetterOfCreditMember_4BF7C5B2C7636684A63AE000868E6B4E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseAndRentalExpense" xlink:label="loc_us-gaap_LeaseAndRentalExpense_E5F13C5F3F90E98E5AADE000868F119A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_us-gaap_LeaseAndRentalExpense_E5F13C5F3F90E98E5AADE000868F119A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubleaseIncome" xlink:label="loc_us-gaap_SubleaseIncome_D979BA53F559B9168FDAE000868FB48D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_us-gaap_SubleaseIncome_D979BA53F559B9168FDAE000868FB48D" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_OperatingLeaseMinimumObligations" xlink:label="loc_dbx_OperatingLeaseMinimumObligations_8339AE2026F46CFAC3DDE000868FAC0D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_dbx_OperatingLeaseMinimumObligations_8339AE2026F46CFAC3DDE000868FAC0D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TenantImprovements" xlink:label="loc_us-gaap_TenantImprovements_B2839EF3836C12B8EA8CE000869077EA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_us-gaap_TenantImprovements_B2839EF3836C12B8EA8CE000869077EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LossContingencyEstimateOfPossibleLoss" xlink:label="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_A7130B4A1A791DF465DFE0008690FB6C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_us-gaap_LossContingencyEstimateOfPossibleLoss_A7130B4A1A791DF465DFE0008690FB6C" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_OperatingLeasesFutureMinimumPaymentsNoLongerObligatedToPay" xlink:label="loc_dbx_OperatingLeasesFutureMinimumPaymentsNoLongerObligatedToPay_760EF7665EDE13E7F0C4E000869066FB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_C4DA4FF9B52AF51C3944E000868F724F" xlink:to="loc_dbx_OperatingLeasesFutureMinimumPaymentsNoLongerObligatedToPay_760EF7665EDE13E7F0C4E000869066FB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CommitmentsAndContingenciesScheduleOfFutureMinimumPaymentsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_F84CE20325515DCEBC8AC25636E177BF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_24B710CCD2F354E689A9116061B24BD8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_F84CE20325515DCEBC8AC25636E177BF" xlink:to="loc_us-gaap_StatementTable_24B710CCD2F354E689A9116061B24BD8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_89F79F54CC7E537485AD535CB5276C27" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_24B710CCD2F354E689A9116061B24BD8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_89F79F54CC7E537485AD535CB5276C27" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_BE901BB192055494F8541F5E72C9B0BA_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_89F79F54CC7E537485AD535CB5276C27" xlink:to="loc_us-gaap_ClassOfStockDomain_BE901BB192055494F8541F5E72C9B0BA_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_AF2B243330BC5F6585AC58C509D8BAF7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_89F79F54CC7E537485AD535CB5276C27" xlink:to="loc_us-gaap_ClassOfStockDomain_AF2B243330BC5F6585AC58C509D8BAF7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_CE0CE6C189215B3D845B4F3131F6CFF4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_AF2B243330BC5F6585AC58C509D8BAF7" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_CE0CE6C189215B3D845B4F3131F6CFF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F84CE20325515DCEBC8AC25636E177BF" xlink:to="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1B63BBDC7AA15475AC7275951C71CE94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_1B63BBDC7AA15475AC7275951C71CE94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_5AD6CA60E9795BC3A829B300FDE01A0B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_5AD6CA60E9795BC3A829B300FDE01A0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_9DF41A8C28D05183935D4C6404166649" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_9DF41A8C28D05183935D4C6404166649" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_B9E869FC50015D4099B2546D502BC2CA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_B9E869FC50015D4099B2546D502BC2CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_011FEA5615705B4182658DF709259E54" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0FB8E3E1C645553DBA7223BB8D683F3D" xlink:to="loc_us-gaap_AssetsCurrent_011FEA5615705B4182658DF709259E54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_751548A9AC025841A9C3C41D85C9728C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_751548A9AC025841A9C3C41D85C9728C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_DFA6089995A85768AF6D5F580D28792A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_DFA6089995A85768AF6D5F580D28792A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_F67233CB2602575CAEA5DA68C8982741" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_Goodwill_F67233CB2602575CAEA5DA68C8982741" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_D6692244B6F9551387F4656D41A80FE7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_D6692244B6F9551387F4656D41A80FE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_77477B5774AC5355A063E6C69766C712" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_2E90DC17B0C45BD7A58BFA7E87EFDFED" xlink:to="loc_us-gaap_Assets_77477B5774AC5355A063E6C69766C712" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_F84CE20325515DCEBC8AC25636E177BF" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:to="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_BA6E93304E015ACA9BE7B23ADD9D80A5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_us-gaap_AccountsPayableCurrent_BA6E93304E015ACA9BE7B23ADD9D80A5" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_AccruedLiabilitiesandOtherLiabilitiesCurrent" xlink:label="loc_dbx_AccruedLiabilitiesandOtherLiabilitiesCurrent_14F999D40A545EA69F73F03CF6F1745C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_dbx_AccruedLiabilitiesandOtherLiabilitiesCurrent_14F999D40A545EA69F73F03CF6F1745C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_6F325D6FCAC154D98A21D9226E8E970F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_6F325D6FCAC154D98A21D9226E8E970F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeaseObligationsCurrent" xlink:label="loc_us-gaap_CapitalLeaseObligationsCurrent_A639D47DE2C457AFAD7CD24E46EEC203" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_us-gaap_CapitalLeaseObligationsCurrent_A639D47DE2C457AFAD7CD24E46EEC203" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_4E98C687595859DD8E48A381C92617EB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_4E98C687595859DD8E48A381C92617EB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_3548907ED8B0545BAD5AD46875ED9E7E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_5FE12706C7A955F1AFD5B34F7813FBF6" xlink:to="loc_us-gaap_LiabilitiesCurrent_3548907ED8B0545BAD5AD46875ED9E7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalLeaseObligationsNoncurrent" xlink:label="loc_us-gaap_CapitalLeaseObligationsNoncurrent_AAF21A1FBF555DFF8519CEE370F94190" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:to="loc_us-gaap_CapitalLeaseObligationsNoncurrent_AAF21A1FBF555DFF8519CEE370F94190" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredRentCreditNoncurrent" xlink:label="loc_us-gaap_DeferredRentCreditNoncurrent_DC12284E87715B61879DA2EED58A0E56" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:to="loc_us-gaap_DeferredRentCreditNoncurrent_DC12284E87715B61879DA2EED58A0E56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_DD9304F0EDA95F8C95F2AD93CE1DC665" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_DD9304F0EDA95F8C95F2AD93CE1DC665" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_DC2B0261047C5350A93E07015F5C26CB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_81E237655C0654CF90A20B3891D334A8" xlink:to="loc_us-gaap_Liabilities_DC2B0261047C5350A93E07015F5C26CB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_A7CC0E50F5E559F0B5AEABEEBE7B4E55" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:to="loc_us-gaap_CommitmentsAndContingencies_A7CC0E50F5E559F0B5AEABEEBE7B4E55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:to="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_47906C7B25455C20A77527BF0F912BC5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_PreferredStockValue_47906C7B25455C20A77527BF0F912BC5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_22FE2D7A00DE51FE90ADDB462F1B4FF1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_CommonStockValue_22FE2D7A00DE51FE90ADDB462F1B4FF1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_173F46B212965D1990F4F78B708415F3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_AdditionalPaidInCapital_173F46B212965D1990F4F78B708415F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_C20641B8F16B5EAB8FCD10F7523ECC6F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_C20641B8F16B5EAB8FCD10F7523ECC6F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_3B3A9503FFDD556786D5A1E0808FEB2B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_3B3A9503FFDD556786D5A1E0808FEB2B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_ED594BBDBD02587BB3DF6E9532B3A1BD" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_05A919912A43564F8191CACB8B8E9B55" xlink:to="loc_us-gaap_StockholdersEquity_ED594BBDBD02587BB3DF6E9532B3A1BD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_E3F14CE8EEE85B1E884C39A81C439477" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_F0213BC5ED3F52A5B327E2B59E26821D" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_E3F14CE8EEE85B1E884C39A81C439477" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfComprehensiveLoss" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfOperations" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/CondensedConsolidatedStatementsOfOperationsParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_6A3AE0C247EA15DDD824DC1C5BAD3F9B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_34A5447410AA523F3759DC1C5BAB8FD6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_6A3AE0C247EA15DDD824DC1C5BAD3F9B" xlink:to="loc_us-gaap_StatementTable_34A5447410AA523F3759DC1C5BAB8FD6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_2D26D172426048C65B9FDC1C5BABCE0E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_34A5447410AA523F3759DC1C5BAB8FD6" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_2D26D172426048C65B9FDC1C5BABCE0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2D26D172426048C65B9FDC1C5BABCE0E" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_2D26D172426048C65B9FDC1C5BABCE0E" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_8549EE0CCF5ECCBCAF68DC1C5BAC3202" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:to="loc_us-gaap_CostOfSalesMember_8549EE0CCF5ECCBCAF68DC1C5BAC3202" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_7F2C954D5C90793608FFDC1C5BACA156" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_7F2C954D5C90793608FFDC1C5BACA156" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_81D7D8E12ECF09C31CC4DC1C5BAD5E1C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_81D7D8E12ECF09C31CC4DC1C5BAD5E1C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_043CC6BA3FB2B3306BD1DC1C5BADD3EF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_C868D8B048C63A71A271DC1C5BABC28D" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_043CC6BA3FB2B3306BD1DC1C5BADD3EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_1E177BA03A588FD5E371DC1C5BAE6E9A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6A3AE0C247EA15DDD824DC1C5BAD3F9B" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_1E177BA03A588FD5E371DC1C5BAE6E9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncashContributionExpense" xlink:label="loc_us-gaap_NoncashContributionExpense_2A6857E145774BF7F79ADC1C5BAEEC2F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6A3AE0C247EA15DDD824DC1C5BAD3F9B" xlink:to="loc_us-gaap_NoncashContributionExpense_2A6857E145774BF7F79ADC1C5BAEEC2F" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CashContributionsToCharitableFoundation" xlink:label="loc_dbx_CashContributionsToCharitableFoundation_525937C093C8C960B5C7DC1C5BAEAD79" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_6A3AE0C247EA15DDD824DC1C5BAD3F9B" xlink:to="loc_dbx_CashContributionsToCharitableFoundation_525937C093C8C960B5C7DC1C5BAEAD79" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockLineItems" xlink:label="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockTable" xlink:label="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_69D5B5037BBDD34A2C22F00873189620" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_StatementClassOfStockAxis_69D5B5037BBDD34A2C22F00873189620" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_69D5B5037BBDD34A2C22F00873189620" xlink:to="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_69D5B5037BBDD34A2C22F00873189620" xlink:to="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_FB471506989A84142673F0087318EE7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_FB471506989A84142673F0087318EE7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_10FA4C5ADDE526A3F23DF0087319FCCB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848" xlink:to="loc_us-gaap_CommonClassBMember_10FA4C5ADDE526A3F23DF0087319FCCB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_B8EC7ADA6D93D2ECBC74F0087319A5DE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_356AB8770D3013991D32F00873189848" xlink:to="loc_us-gaap_CommonClassAMember_B8EC7ADA6D93D2ECBC74F0087319A5DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_3DC0AF7D9096013CC182F0087319DF39" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_3DC0AF7D9096013CC182F0087319DF39" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_3DC0AF7D9096013CC182F0087319DF39" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_3DC0AF7D9096013CC182F0087319DF39" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrivatePlacementMember" xlink:label="loc_us-gaap_PrivatePlacementMember_6ADCFFC77BA75897AABFF008731A9147" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722" xlink:to="loc_us-gaap_PrivatePlacementMember_6ADCFFC77BA75897AABFF008731A9147" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OverAllotmentOptionMember" xlink:label="loc_us-gaap_OverAllotmentOptionMember_20639392114EF74A5400F008731A6332" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_1F65ECEB1480C1F08631F008731AB722" xlink:to="loc_us-gaap_OverAllotmentOptionMember_20639392114EF74A5400F008731A6332" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_2C53967F5BAC27ECBC8DF008731B9BC3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_2C53967F5BAC27ECBC8DF008731B9BC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockNameDomain" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_2C53967F5BAC27ECBC8DF008731B9BC3" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockNameDomain" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_2C53967F5BAC27ECBC8DF008731B9BC3" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember" xlink:label="loc_dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember_DE6C5C092A258B7001A1F008731B5E1C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439" xlink:to="loc_dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember_DE6C5C092A258B7001A1F008731B5E1C" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember" xlink:label="loc_dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember_4F16AC2BA18E4AC6566CF008731B9904" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439" xlink:to="loc_dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember_4F16AC2BA18E4AC6566CF008731B9904" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ConversionOfClassBCommonStockToClassACommonStockMember" xlink:label="loc_dbx_ConversionOfClassBCommonStockToClassACommonStockMember_271CF670C3CBD6295701F0087321B990" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_049A12D3C13F42E07916F008731B0439" xlink:to="loc_dbx_ConversionOfClassBCommonStockToClassACommonStockMember_271CF670C3CBD6295701F0087321B990" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_41DBA17B344DD55A9A82F0087321CD85" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_RangeAxis_41DBA17B344DD55A9A82F0087321CD85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_41DBA17B344DD55A9A82F0087321CD85" xlink:to="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_41DBA17B344DD55A9A82F0087321CD85" xlink:to="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_DE669A28D9872908B21BF0087322B30B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A" xlink:to="loc_us-gaap_MinimumMember_DE669A28D9872908B21BF0087322B30B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_C2F3C0318A9F0DB91458F0087322F261" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_DC0CA63E9E9F9FA61AE9F0087322C85A" xlink:to="loc_us-gaap_MaximumMember_C2F3C0318A9F0DB91458F0087322F261" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_5190143EE89083B4D269F0087322F63E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_AwardTypeAxis_5190143EE89083B4D269F0087322F63E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_5190143EE89083B4D269F0087322F63E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_5190143EE89083B4D269F0087322F63E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_TwoTierRestrictedStockUnitsRSUsMember" xlink:label="loc_dbx_TwoTierRestrictedStockUnitsRSUsMember_71ACE680AF0BC0CC8211F0087323F16B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:to="loc_dbx_TwoTierRestrictedStockUnitsRSUsMember_71ACE680AF0BC0CC8211F0087323F16B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_CF8232AA359DC5E88854F00873249052" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_CF8232AA359DC5E88854F00873249052" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_OneTierRestrictedStockUnitsRSUsMember" xlink:label="loc_dbx_OneTierRestrictedStockUnitsRSUsMember_5E4433938BCC197874C0F00873248359" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:to="loc_dbx_OneTierRestrictedStockUnitsRSUsMember_5E4433938BCC197874C0F00873248359" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_1FB003FD5C3D0E6FEA16F0087324109D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_296A0338F52D4B9A7DF2F0087323EB24" xlink:to="loc_us-gaap_RestrictedStockMember_1FB003FD5C3D0E6FEA16F0087324109D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_225C5A8FAB4E014811A6F0087324F779" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_PlanNameAxis_225C5A8FAB4E014811A6F0087324F779" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_39ADE7BC3C80AF1C0594F00873247CA7_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_225C5A8FAB4E014811A6F0087324F779" xlink:to="loc_us-gaap_PlanNameDomain_39ADE7BC3C80AF1C0594F00873247CA7_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_39ADE7BC3C80AF1C0594F00873247CA7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_225C5A8FAB4E014811A6F0087324F779" xlink:to="loc_us-gaap_PlanNameDomain_39ADE7BC3C80AF1C0594F00873247CA7" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CoFounderGrantsMember" xlink:label="loc_dbx_CoFounderGrantsMember_EFDD8118D95B76227A29F0087325E719" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_39ADE7BC3C80AF1C0594F00873247CA7" xlink:to="loc_dbx_CoFounderGrantsMember_EFDD8118D95B76227A29F0087325E719" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_DA5EAE105319F6AE4833F0087325CDD7" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_TitleOfIndividualAxis_DA5EAE105319F6AE4833F0087325CDD7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_DA5EAE105319F6AE4833F0087325CDD7" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_DA5EAE105319F6AE4833F0087325CDD7" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChiefExecutiveOfficerMember" xlink:label="loc_us-gaap_ChiefExecutiveOfficerMember_863BAEC9C45012C407D0F00873267C71" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A" xlink:to="loc_us-gaap_ChiefExecutiveOfficerMember_863BAEC9C45012C407D0F00873267C71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DirectorMember" xlink:label="loc_us-gaap_DirectorMember_D859F204EF63C9AC075CF008732663FC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_4630D4F8D024C33960BFF00873254F4A" xlink:to="loc_us-gaap_DirectorMember_D859F204EF63C9AC075CF008732663FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_421B1495971086BDE809F008732627F8" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_VestingAxis_421B1495971086BDE809F008732627F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_FB516E94C467EB278FE5F00873269DB9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_421B1495971086BDE809F008732627F8" xlink:to="loc_us-gaap_VestingDomain_FB516E94C467EB278FE5F00873269DB9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_FB516E94C467EB278FE5F00873269DB9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_421B1495971086BDE809F008732627F8" xlink:to="loc_us-gaap_VestingDomain_FB516E94C467EB278FE5F00873269DB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_12752BCF909FD2C3E966F00873272465" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_FB516E94C467EB278FE5F00873269DB9" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_12752BCF909FD2C3E966F00873272465" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_F310B414CBFCFF2A8945F0087327AC00" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_F310B414CBFCFF2A8945F0087327AC00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_F4A518103A9B5AE2AC93F0087327F791_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_F310B414CBFCFF2A8945F0087327AC00" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_F4A518103A9B5AE2AC93F0087327F791_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_F4A518103A9B5AE2AC93F0087327F791" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_F310B414CBFCFF2A8945F0087327AC00" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_F4A518103A9B5AE2AC93F0087327F791" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_85EB69CA855AD7F1893EF00873281C3F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_F4A518103A9B5AE2AC93F0087327F791" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_85EB69CA855AD7F1893EF00873281C3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_06BB467C48C499BF8CA0F00873281DB4" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_06BB467C48C499BF8CA0F00873281DB4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_CED3C6AB923D12107062F00873288225_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_06BB467C48C499BF8CA0F00873281DB4" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_CED3C6AB923D12107062F00873288225_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_CED3C6AB923D12107062F00873288225" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_06BB467C48C499BF8CA0F00873281DB4" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_CED3C6AB923D12107062F00873288225" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_AccountsReceivableAndOtherReceivableMember" xlink:label="loc_dbx_AccountsReceivableAndOtherReceivableMember_7A14F9B28965A8800F80F0087328C9B7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_CED3C6AB923D12107062F00873288225" xlink:to="loc_dbx_AccountsReceivableAndOtherReceivableMember_7A14F9B28965A8800F80F0087328C9B7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorCustomersAxis" xlink:label="loc_us-gaap_MajorCustomersAxis_00C8AC2EB6EE760AB693F00873298FB5" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_MajorCustomersAxis_00C8AC2EB6EE760AB693F00873298FB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorCustomersAxis_00C8AC2EB6EE760AB693F00873298FB5" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorCustomersAxis_00C8AC2EB6EE760AB693F00873298FB5" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CustomerAMember" xlink:label="loc_dbx_CustomerAMember_8A120F8487EA3633D856F00873297DE7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E" xlink:to="loc_dbx_CustomerAMember_8A120F8487EA3633D856F00873297DE7" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CustomerBMember" xlink:label="loc_dbx_CustomerBMember_13C3EF54F3117DAE36B8F0087329E36B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_9D61BABB7699E7D140D5F0087329DB5E" xlink:to="loc_dbx_CustomerBMember_13C3EF54F3117DAE36B8F0087329E36B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostAxis" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_F53AA483B8609F570295F008732A850A" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_F53AA483B8609F570295F008732A850A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostDomain" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_5C0D156BA1E681168935F008732ABDA9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_F53AA483B8609F570295F008732A850A" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_5C0D156BA1E681168935F008732ABDA9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostDomain" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_5C0D156BA1E681168935F008732ABDA9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_F53AA483B8609F570295F008732A850A" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_5C0D156BA1E681168935F008732ABDA9" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_DeferredCommissionsMember" xlink:label="loc_dbx_DeferredCommissionsMember_EB22B1977E0AF1581D7FF008732A2C7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_5C0D156BA1E681168935F008732ABDA9" xlink:to="loc_dbx_DeferredCommissionsMember_EB22B1977E0AF1581D7FF008732A2C7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_E31E98F2AF6D0B4CE22FF008732FB233" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_E31E98F2AF6D0B4CE22FF008732FB233" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_E31E98F2AF6D0B4CE22FF008732FB233" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_E31E98F2AF6D0B4CE22FF008732FB233" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_7278099DDD89B8F5E28FF0087330FC9B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_7278099DDD89B8F5E28FF0087330FC9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentAssetsMember" xlink:label="loc_us-gaap_OtherNoncurrentAssetsMember_869D34CCADAA67720C87F008733089EC" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:to="loc_us-gaap_OtherNoncurrentAssetsMember_869D34CCADAA67720C87F008733089EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccruedLiabilitiesMember" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_553A56183EA41FDD5469F0087330B90B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_553A56183EA41FDD5469F0087330B90B" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_DeferredRentNonCurrentMember" xlink:label="loc_dbx_DeferredRentNonCurrentMember_A2FA7F50DA22ED01366DF00873317FBA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D12B214DAABA116B1014F00873309AAF" xlink:to="loc_dbx_DeferredRentNonCurrentMember_A2FA7F50DA22ED01366DF00873317FBA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8220804CA16DEE8C3BBCF008733127C9" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8220804CA16DEE8C3BBCF008733127C9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A4A3392E030948E20D6BF00873314907_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8220804CA16DEE8C3BBCF008733127C9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A4A3392E030948E20D6BF00873314907_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A4A3392E030948E20D6BF00873314907" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_8220804CA16DEE8C3BBCF008733127C9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A4A3392E030948E20D6BF00873314907" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_InfrastructureEquipmentMember" xlink:label="loc_dbx_InfrastructureEquipmentMember_E6756E2C0AFB6DAB3DE7F0087331DB3E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_A4A3392E030948E20D6BF00873314907" xlink:to="loc_dbx_InfrastructureEquipmentMember_E6756E2C0AFB6DAB3DE7F0087331DB3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_F54128DBC402C5ABF73BF00873322EA8" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConversionOfStockTable_AA57E277F1BE09BF5F5BF0087317E407" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_F54128DBC402C5ABF73BF00873322EA8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_4FD91B511A874223F9EAF008733394B1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_F54128DBC402C5ABF73BF00873322EA8" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_4FD91B511A874223F9EAF008733394B1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_4FD91B511A874223F9EAF008733394B1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_F54128DBC402C5ABF73BF00873322EA8" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_4FD91B511A874223F9EAF008733394B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChangeInAccountingMethodAccountedForAsChangeInEstimateMember" xlink:label="loc_us-gaap_ChangeInAccountingMethodAccountedForAsChangeInEstimateMember_CF6BF2230EE8A9B583BEF00873339A6B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_4FD91B511A874223F9EAF008733394B1" xlink:to="loc_us-gaap_ChangeInAccountingMethodAccountedForAsChangeInEstimateMember_CF6BF2230EE8A9B583BEF00873339A6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenuePerformanceObligationDescriptionOfTiming" xlink:label="loc_us-gaap_RevenuePerformanceObligationDescriptionOfTiming_11C82E418A0CDB358D40F0263AB0E8C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_RevenuePerformanceObligationDescriptionOfTiming_11C82E418A0CDB358D40F0263AB0E8C7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_02B3DA0579C3A29B4685F0087334CD4F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_02B3DA0579C3A29B4685F0087334CD4F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="loc_us-gaap_SharesIssuedPricePerShare_2894BEE081BDB2B164AEF00873346A2C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_SharesIssuedPricePerShare_2894BEE081BDB2B164AEF00873346A2C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_EED9712908972D0107F0F0087334FAAD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_EED9712908972D0107F0F0087334FAAD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_0829FB7CE889AB1D1104F00873348E92" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_0829FB7CE889AB1D1104F00873348E92" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_EC3F883E7F34A394334EF00873354009" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_EC3F883E7F34A394334EF00873354009" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="loc_us-gaap_ConversionOfStockSharesIssued1_766C4776676E40A6778EF00873356714" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ConversionOfStockSharesIssued1_766C4776676E40A6778EF00873356714" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_92C54E97F57FC87CB3C7F00873350BAE" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_92C54E97F57FC87CB3C7F00873350BAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_C0915A2312BA386C012BF00873361760" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_C0915A2312BA386C012BF00873361760" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_7B9F477C428EF540C990F008733617D3" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_7B9F477C428EF540C990F008733617D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_77FD36945BB3DC4625B7F0087336C35A" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost_77FD36945BB3DC4625B7F0087336C35A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01B962E12802D8EDBCC4F00873364914" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_01B962E12802D8EDBCC4F00873364914" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_09A3F9E561DCCF64D35CF00873373A76" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_09A3F9E561DCCF64D35CF00873373A76" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber_0F89262AA955A0F72900F00873374C5E" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber_0F89262AA955A0F72900F00873374C5E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LaborAndRelatedExpense" xlink:label="loc_us-gaap_LaborAndRelatedExpense_515CF1919215F7121948F008733753B0" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_LaborAndRelatedExpense_515CF1919215F7121948F008733753B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_AB166B12C93387902C67F0087338F1D4" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_AB166B12C93387902C67F0087338F1D4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_74E1647299AE1E9ACC66F00873392F44" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_74E1647299AE1E9ACC66F00873392F44" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_E23F7E6A35567F5A1D47F00873390040" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_E23F7E6A35567F5A1D47F00873390040" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardTypes" xlink:label="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardTypes_0B79924BA512F7727975F0087339DF53" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardTypes_0B79924BA512F7727975F0087339DF53" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_EDBF880638F5B049EBE4F00873394D54" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_EDBF880638F5B049EBE4F00873394D54" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_68776D7010DBDD7CE9CDF0087339F173" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_68776D7010DBDD7CE9CDF0087339F173" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches" xlink:label="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches_0AA9FE21844009F63EDCF008733ACAC8" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches_0AA9FE21844009F63EDCF008733ACAC8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_7F4E993C257072D1DDBDF008733FBF3E" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_7F4E993C257072D1DDBDF008733FBF3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_9B82AA09CAFA2867DD3EF00873406499" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_9B82AA09CAFA2867DD3EF00873406499" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_0A75F401781777438007F00873403321" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_0A75F401781777438007F00873403321" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_D3D3C8D5D56BBDCE61CCF0087340954C" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_D3D3C8D5D56BBDCE61CCF0087340954C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NontradeReceivablesCurrent" xlink:label="loc_us-gaap_NontradeReceivablesCurrent_77C0A2F6B8CC47C81B65F0087340ED06" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_NontradeReceivablesCurrent_77C0A2F6B8CC47C81B65F0087340ED06" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_TenantImprovementAllowanceReceivableIncludedInCurrentAssets" xlink:label="loc_dbx_TenantImprovementAllowanceReceivableIncludedInCurrentAssets_361378F9877ABB35A88AF035E584BFA8" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_TenantImprovementAllowanceReceivableIncludedInCurrentAssets_361378F9877ABB35A88AF035E584BFA8" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CapitalizedContractCostsAdditions" xlink:label="loc_dbx_CapitalizedContractCostsAdditions_13A3886F417E0530DDC5F0087341DE03" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_CapitalizedContractCostsAdditions_13A3886F417E0530DDC5F0087341DE03" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostNet" xlink:label="loc_us-gaap_CapitalizedContractCostNet_7FD17EDFF4FC504977D4F0087341A72A" xlink:type="locator" />
    <link:definitionArc order="30" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_CapitalizedContractCostNet_7FD17EDFF4FC504977D4F0087341A72A" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CapitalizedContractCostAmortizationPeriod" xlink:label="loc_dbx_CapitalizedContractCostAmortizationPeriod_3C45E4E099E53E12853FF00873411833" xlink:type="locator" />
    <link:definitionArc order="31" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_CapitalizedContractCostAmortizationPeriod_3C45E4E099E53E12853FF00873411833" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AmortizationOfDeferredSalesCommissions" xlink:label="loc_us-gaap_AmortizationOfDeferredSalesCommissions_E7C60344F10D51E24B5FF0087341FBDC" xlink:type="locator" />
    <link:definitionArc order="32" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_AmortizationOfDeferredSalesCommissions_E7C60344F10D51E24B5FF0087341FBDC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CapitalizedContractCostImpairmentLoss" xlink:label="loc_us-gaap_CapitalizedContractCostImpairmentLoss_D14F9A88ECDD433DB510F0087342D7B0" xlink:type="locator" />
    <link:definitionArc order="33" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_CapitalizedContractCostImpairmentLoss_D14F9A88ECDD433DB510F0087342D7B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_1FBFB764451A3EDDB2C7F0087342BFFE" xlink:type="locator" />
    <link:definitionArc order="34" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_1FBFB764451A3EDDB2C7F0087342BFFE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_D761BF18D9060D59AEDFF0087342DDB9" xlink:type="locator" />
    <link:definitionArc order="35" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_us-gaap_Depreciation_D761BF18D9060D59AEDFF0087342DDB9" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_LeaseIncentiveObligation" xlink:label="loc_dbx_LeaseIncentiveObligation_5EEEDCDFA66ED65A0EEAF00873423318" xlink:type="locator" />
    <link:definitionArc order="36" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockLineItems_1004E23E117264B1A441F0087333930C" xlink:to="loc_dbx_LeaseIncentiveObligation_5EEEDCDFA66ED65A0EEAF00873423318" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPerformanceObligationsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_C72055DF98DD57998ECBE3EC8BB20CEA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2AAC48B19AA1563286C988F3EEA3C672" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_C72055DF98DD57998ECBE3EC8BB20CEA" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2AAC48B19AA1563286C988F3EEA3C672" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_FA646D7E7CB25040885E8EC65CE6567D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2AAC48B19AA1563286C988F3EEA3C672" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_FA646D7E7CB25040885E8EC65CE6567D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod_6FC38848F61856B99CDEC369839B252A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_C72055DF98DD57998ECBE3EC8BB20CEA" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod_6FC38848F61856B99CDEC369839B252A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLivesOfPropertyAndEquipmentDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_2078611EC350553CB105270D95800B2D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_89F88885BB525A1EA059033619B8DEAD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_2078611EC350553CB105270D95800B2D" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_89F88885BB525A1EA059033619B8DEAD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_2778E92A2CEE5469A1E456A05FEE483E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_89F88885BB525A1EA059033619B8DEAD" xlink:to="loc_us-gaap_RangeAxis_2778E92A2CEE5469A1E456A05FEE483E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_E242F33303E1453349F98F7AFF902B66_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_2778E92A2CEE5469A1E456A05FEE483E" xlink:to="loc_us-gaap_RangeMember_E242F33303E1453349F98F7AFF902B66_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_FF8D7B115C9B510B8A40C445B0512380" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_2778E92A2CEE5469A1E456A05FEE483E" xlink:to="loc_us-gaap_RangeMember_FF8D7B115C9B510B8A40C445B0512380" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_B5C3150819B358C5A6981E4EBEE72AAC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_FF8D7B115C9B510B8A40C445B0512380" xlink:to="loc_us-gaap_MinimumMember_B5C3150819B358C5A6981E4EBEE72AAC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_0C350A957CBA5DE18605FEE13476B1E5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_FF8D7B115C9B510B8A40C445B0512380" xlink:to="loc_us-gaap_MaximumMember_0C350A957CBA5DE18605FEE13476B1E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_5C512BCE70FA5FECBFFD7C8A84A4EF75" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_89F88885BB525A1EA059033619B8DEAD" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_5C512BCE70FA5FECBFFD7C8A84A4EF75" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_13E081F2F1A6052C97C68F7AFF901A09_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_5C512BCE70FA5FECBFFD7C8A84A4EF75" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_13E081F2F1A6052C97C68F7AFF901A09_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_021FA3449AA757B7968333C379432F94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_5C512BCE70FA5FECBFFD7C8A84A4EF75" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_021FA3449AA757B7968333C379432F94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BuildingMember" xlink:label="loc_us-gaap_BuildingMember_60580341BF7A58878A962E98476C56E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_021FA3449AA757B7968333C379432F94" xlink:to="loc_us-gaap_BuildingMember_60580341BF7A58878A962E98476C56E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember_890922A43314569F9823FB876CC46141" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_021FA3449AA757B7968333C379432F94" xlink:to="loc_us-gaap_ComputerEquipmentMember_890922A43314569F9823FB876CC46141" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OfficeEquipmentMember" xlink:label="loc_us-gaap_OfficeEquipmentMember_35F6BF35E8F051C2B83BC328B3EA0D39" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_021FA3449AA757B7968333C379432F94" xlink:to="loc_us-gaap_OfficeEquipmentMember_35F6BF35E8F051C2B83BC328B3EA0D39" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_30A52888573B5F13808DD748CA93D65B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_2078611EC350553CB105270D95800B2D" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_30A52888573B5F13808DD748CA93D65B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DescriptionOfBusinessAndSummaryOfSignificantAccountingPoliciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentInformationLineItems" xlink:label="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentInformationTable" xlink:label="loc_dei_DocumentInformationTable_F14E71C741C45FA281E67E642097E0D6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_DocumentInformationTable_F14E71C741C45FA281E67E642097E0D6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_124AFAA885365826BC792E2386BB990C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_F14E71C741C45FA281E67E642097E0D6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_124AFAA885365826BC792E2386BB990C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_64D15DFF399C46507CF18F7AFEF0F8C1_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_124AFAA885365826BC792E2386BB990C" xlink:to="loc_us-gaap_ClassOfStockDomain_64D15DFF399C46507CF18F7AFEF0F8C1_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_02EB5D17AE9151F8B3C16E5EE1DBD5A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_124AFAA885365826BC792E2386BB990C" xlink:to="loc_us-gaap_ClassOfStockDomain_02EB5D17AE9151F8B3C16E5EE1DBD5A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_30941ECAB6D25AED89150645C230FBFB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_02EB5D17AE9151F8B3C16E5EE1DBD5A9" xlink:to="loc_us-gaap_CommonClassAMember_30941ECAB6D25AED89150645C230FBFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_DA51803EE7DB52349AC6681AF425B9FF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_02EB5D17AE9151F8B3C16E5EE1DBD5A9" xlink:to="loc_us-gaap_CommonClassBMember_DA51803EE7DB52349AC6681AF425B9FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassCMember" xlink:label="loc_us-gaap_CommonClassCMember_CDE5E528C92C5D2CBF2DB7E398B5F5F7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_02EB5D17AE9151F8B3C16E5EE1DBD5A9" xlink:to="loc_us-gaap_CommonClassCMember_CDE5E528C92C5D2CBF2DB7E398B5F5F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_6637EC1061465FAD853AF9979A8930E2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_EntityRegistrantName_6637EC1061465FAD853AF9979A8930E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_28B4F4BFB1B3596D9702AF6F80E63563" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_EntityCentralIndexKey_28B4F4BFB1B3596D9702AF6F80E63563" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_4CE316481F4E54EDBB2BB73E79AFBB9D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_CurrentFiscalYearEndDate_4CE316481F4E54EDBB2BB73E79AFBB9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_1F7BCFE4591853E8A0CA985E8B271EC6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_EntityFilerCategory_1F7BCFE4591853E8A0CA985E8B271EC6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_FB04B70923185284A9C37CBFBFA0170C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_DocumentType_FB04B70923185284A9C37CBFBFA0170C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_24866709FCE8596A9D0661509405E60D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_DocumentPeriodEndDate_24866709FCE8596A9D0661509405E60D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_39B5B08D2C015877A94C0B5251B7F5DE" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_DocumentFiscalYearFocus_39B5B08D2C015877A94C0B5251B7F5DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_9BA27B8354725582BD049819BE127D7D" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_DocumentFiscalPeriodFocus_9BA27B8354725582BD049819BE127D7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_EB1E83B5AB685868A99C04D1E02A0A2D" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_AmendmentFlag_EB1E83B5AB685868A99C04D1E02A0A2D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_CD6391855FB85C4C85970FA3A6927526" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_CC4F29F5977D56039DBC0971E5603091" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_CD6391855FB85C4C85970FA3A6927526" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/FairValueMeasurements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_8DD170239409EC5A66A3E0008705DDE8" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_8DD170239409EC5A66A3E0008705DDE8" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9F526B3A36B1DDD7131DE000870151AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9F526B3A36B1DDD7131DE000870151AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_186BA479D2735F47A192E00087018039_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9F526B3A36B1DDD7131DE000870151AE" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_186BA479D2735F47A192E00087018039_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_186BA479D2735F47A192E00087018039" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9F526B3A36B1DDD7131DE000870151AE" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_186BA479D2735F47A192E00087018039" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_C5EF987046094FC8DB5EE0008701B123" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_186BA479D2735F47A192E00087018039" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_C5EF987046094FC8DB5EE0008701B123" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CA490E04E11230DE8B13E00087016741" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CA490E04E11230DE8B13E00087016741" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CA490E04E11230DE8B13E00087016741" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_CA490E04E11230DE8B13E00087016741" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_0A2D0B8412AE5CA37462E0008702DB49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_0A2D0B8412AE5CA37462E0008702DB49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_21E1DFF5E5BA6D8196A0E000870219B1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_21E1DFF5E5BA6D8196A0E000870219B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_86EF816F0CAB0B21A311E00087022A6C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1387395D5E731F3A1694E000870278C4" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_86EF816F0CAB0B21A311E00087022A6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_505AEB3040E25397A087E00087034D51" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_505AEB3040E25397A087E00087034D51" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_505AEB3040E25397A087E00087034D51" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_505AEB3040E25397A087E00087034D51" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="loc_us-gaap_MoneyMarketFundsMember_44B462E3C8437826AF30E000870327A8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705" xlink:to="loc_us-gaap_MoneyMarketFundsMember_44B462E3C8437826AF30E000870327A8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_C672B23003B2D97493F9E0008703D0E3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705" xlink:to="loc_us-gaap_CommercialPaperMember_C672B23003B2D97493F9E0008703D0E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashEquivalentsMember" xlink:label="loc_us-gaap_CashEquivalentsMember_89B5472A67DABA3CFCB7E00087042900" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_1078D5984EAA8D973A78E0008703D705" xlink:to="loc_us-gaap_CashEquivalentsMember_89B5472A67DABA3CFCB7E00087042900" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="loc_us-gaap_FinancialInstrumentAxis_015EB48B3A6A4E1D1C3AE0008704914A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_980EF6850E1CBF1E971FE0008700D1F0" xlink:to="loc_us-gaap_FinancialInstrumentAxis_015EB48B3A6A4E1D1C3AE0008704914A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_015EB48B3A6A4E1D1C3AE0008704914A" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_015EB48B3A6A4E1D1C3AE0008704914A" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_B62FF578A89F249AC575E0008704C0E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_B62FF578A89F249AC575E0008704C0E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USTreasurySecuritiesMember" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_106C107646867D2B1963E00087055A93" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_106C107646867D2B1963E00087055A93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="loc_us-gaap_CertificatesOfDepositMember_2CBBA75147C5490EE62DE00087051668" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:to="loc_us-gaap_CertificatesOfDepositMember_2CBBA75147C5490EE62DE00087051668" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_5EF1790C9005FC4F021EE00087054351" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:to="loc_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember_5EF1790C9005FC4F021EE00087054351" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_6F1DFF0EB067F0F18A0DE0008705C6C3" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_EF87868D866F2D75722CE00087044458" xlink:to="loc_us-gaap_CommercialPaperMember_6F1DFF0EB067F0F18A0DE0008705C6C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_830BE22CC1A5A033C8D0E0008706EAEB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_8DD170239409EC5A66A3E0008705DDE8" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_830BE22CC1A5A033C8D0E0008706EAEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_E051901EA1AA229E4A77E00087060B2A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_8DD170239409EC5A66A3E0008705DDE8" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_E051901EA1AA229E4A77E00087060B2A" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CashEquivalentsandShorttermInvestments" xlink:label="loc_dbx_CashEquivalentsandShorttermInvestments_5A469D959B669E56A712E0008706CC89" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_8DD170239409EC5A66A3E0008705DDE8" xlink:to="loc_dbx_CashEquivalentsandShorttermInvestments_5A469D959B669E56A712E0008706CC89" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/FairValueMeasurementsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/GeographicAreas" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/GeographicAreasDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_78AEFCCF85885797918179C8064F9E4F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_CD01E01BBEAA53D0B8B3494D9EF0ADF4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_78AEFCCF85885797918179C8064F9E4F" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_CD01E01BBEAA53D0B8B3494D9EF0ADF4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_0DC94BDC342B54D183B0B1A5D2EB1749" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_CD01E01BBEAA53D0B8B3494D9EF0ADF4" xlink:to="loc_us-gaap_StatementGeographicalAxis_0DC94BDC342B54D183B0B1A5D2EB1749" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_0C5D3D76DFF18C73EED4C820FDFF867C_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_0DC94BDC342B54D183B0B1A5D2EB1749" xlink:to="loc_us-gaap_SegmentGeographicalDomain_0C5D3D76DFF18C73EED4C820FDFF867C_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_238BB931DDE259D78CC6C0C24F166F32" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_0DC94BDC342B54D183B0B1A5D2EB1749" xlink:to="loc_us-gaap_SegmentGeographicalDomain_238BB931DDE259D78CC6C0C24F166F32" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:label="loc_country_US_5B050A44B77158DE8E20DFC9C9FCC4C4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_238BB931DDE259D78CC6C0C24F166F32" xlink:to="loc_country_US_5B050A44B77158DE8E20DFC9C9FCC4C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NonUsMember" xlink:label="loc_us-gaap_NonUsMember_31F0A37B8A9D5F0AACC48B2A0812F8DF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_238BB931DDE259D78CC6C0C24F166F32" xlink:to="loc_us-gaap_NonUsMember_31F0A37B8A9D5F0AACC48B2A0812F8DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_BE83EA08856A5E8B9CB5C390FB4BDE25" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_78AEFCCF85885797918179C8064F9E4F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_BE83EA08856A5E8B9CB5C390FB4BDE25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_3CCC849332885C6295F1E77AB4F30581" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_78AEFCCF85885797918179C8064F9E4F" xlink:to="loc_us-gaap_Revenues_3CCC849332885C6295F1E77AB4F30581" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/GeographicAreasTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/Goodwill" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/GoodwillDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/IncomeTaxesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/NetLossPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/NetLossPerShareScheduleOfEarningsPerShareBasicAndDilutedDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_51909050D109512C97F123F84CC60472" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_4038A56ECB035AAF9C20F615A9626A1B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_51909050D109512C97F123F84CC60472" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_4038A56ECB035AAF9C20F615A9626A1B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_980F23427E19535FB9409D20AFE021B8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_4038A56ECB035AAF9C20F615A9626A1B" xlink:to="loc_us-gaap_StatementClassOfStockAxis_980F23427E19535FB9409D20AFE021B8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_044C87064648D61B2B8FC820FE6F1048_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_980F23427E19535FB9409D20AFE021B8" xlink:to="loc_us-gaap_ClassOfStockDomain_044C87064648D61B2B8FC820FE6F1048_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_702FD2D3A9095160902353EB2605A6C3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_980F23427E19535FB9409D20AFE021B8" xlink:to="loc_us-gaap_ClassOfStockDomain_702FD2D3A9095160902353EB2605A6C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_3197B157F9D4596B9A21E6DA25FDED91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_702FD2D3A9095160902353EB2605A6C3" xlink:to="loc_us-gaap_CommonClassAMember_3197B157F9D4596B9A21E6DA25FDED91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_2C95610566D05F4280E25099C3AF926C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_702FD2D3A9095160902353EB2605A6C3" xlink:to="loc_us-gaap_CommonClassBMember_2C95610566D05F4280E25099C3AF926C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_A2D4A3F1F9735F969B5EF57A440BFD7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_51909050D109512C97F123F84CC60472" xlink:to="loc_us-gaap_NetIncomeLoss_A2D4A3F1F9735F969B5EF57A440BFD7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted" xlink:label="loc_us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_5B4291F848DB5FBE8C5950E84C5DB95C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_51909050D109512C97F123F84CC60472" xlink:to="loc_us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted_5B4291F848DB5FBE8C5950E84C5DB95C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDiluted_9643D90DFFC25FDB9016DB00F2DC9723" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_51909050D109512C97F123F84CC60472" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDiluted_9643D90DFFC25FDB9016DB00F2DC9723" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/NetLossPerShareScheduleOfPotentiallyDilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_31B4A030CE8E50B6891B96881F244041" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_79ECA25DBFD35CA393ED9CF26FC8EE08" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_31B4A030CE8E50B6891B96881F244041" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_79ECA25DBFD35CA393ED9CF26FC8EE08" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_B9BDCAFD7825500591B1AE704731DE6E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_79ECA25DBFD35CA393ED9CF26FC8EE08" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_B9BDCAFD7825500591B1AE704731DE6E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6CA6BF9661357C3A8AC8C820FE5D2494_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_B9BDCAFD7825500591B1AE704731DE6E" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_6CA6BF9661357C3A8AC8C820FE5D2494_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_B9BDCAFD7825500591B1AE704731DE6E" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_E85876CE87395A0D94428CD1FFBDAEC4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_E85876CE87395A0D94428CD1FFBDAEC4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_454CCD54227A5947956A38E2D97B4033" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_454CCD54227A5947956A38E2D97B4033" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_798B639899E85BDC8F1C1E0359C111D5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:to="loc_us-gaap_EmployeeStockOptionMember_798B639899E85BDC8F1C1E0359C111D5" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CoFounderGrantsMember" xlink:label="loc_dbx_CoFounderGrantsMember_157648C9688A563B809FB9B2290D9B26" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:to="loc_dbx_CoFounderGrantsMember_157648C9688A563B809FB9B2290D9B26" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_SharesSubjectToRepurchaseMember" xlink:label="loc_dbx_SharesSubjectToRepurchaseMember_D1AE75FC44605C9FAF4FBF446E20B96D" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_2D338A9A0EE2593C9BD1CCAA2BB37E55" xlink:to="loc_dbx_SharesSubjectToRepurchaseMember_D1AE75FC44605C9FAF4FBF446E20B96D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_E680533D1D2653CD855F27CAC6C9BC3D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_31B4A030CE8E50B6891B96881F244041" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_E680533D1D2653CD855F27CAC6C9BC3D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/NetLossPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/PropertyAndEquipmentNet" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/PropertyAndEquipmentNetNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_18E91F7096696D17DFC1F00872363891" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_18E91F7096696D17DFC1F00872363891" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_6AD431B519E2F877C671F0087236A5D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_18E91F7096696D17DFC1F00872363891" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_6AD431B519E2F877C671F0087236A5D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6AD431B519E2F877C671F0087236A5D3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6AD431B519E2F877C671F0087236A5D3" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherCurrentLiabilitiesMember" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_B778A8D2DA16DF53D593F0087236E080" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_B778A8D2DA16DF53D593F0087236E080" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_3700A68ABE0CB86AEBDAF0087237EC59" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_D37A29F3B54458D58BD2F0087236BA29" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_3700A68ABE0CB86AEBDAF0087237EC59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_A91A02C07896659071B6F0087237B475" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_18E91F7096696D17DFC1F00872363891" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_A91A02C07896659071B6F0087237B475" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_A91A02C07896659071B6F0087237B475" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_A91A02C07896659071B6F0087237B475" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BuildingMember" xlink:label="loc_us-gaap_BuildingMember_49D058EC6A33A2CF944BF02DA4F45EB3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD" xlink:to="loc_us-gaap_BuildingMember_49D058EC6A33A2CF944BF02DA4F45EB3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsHeldUnderCapitalLeasesMember" xlink:label="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_ACFB9BE61C8BC2BA2ACEF00872389988" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_CDC6612C8A661E68D26AF0087237F2DD" xlink:to="loc_us-gaap_AssetsHeldUnderCapitalLeasesMember_ACFB9BE61C8BC2BA2ACEF00872389988" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_PropertyPlantandEquipmentGrossAmountDerecognized" xlink:label="loc_dbx_PropertyPlantandEquipmentGrossAmountDerecognized_5269A37399B77BA3782AF008723879E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_dbx_PropertyPlantandEquipmentGrossAmountDerecognized_5269A37399B77BA3782AF008723879E9" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_AccumulatedDepreciationDepletionandAmortizationPropertyPlantandEquipmentDerecognized" xlink:label="loc_dbx_AccumulatedDepreciationDepletionandAmortizationPropertyPlantandEquipmentDerecognized_D1A0CE111AA562C0440EF0087238425C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_dbx_AccumulatedDepreciationDepletionandAmortizationPropertyPlantandEquipmentDerecognized_D1A0CE111AA562C0440EF0087238425C" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ImputedFinancingLeaseObligationDerecognized" xlink:label="loc_dbx_ImputedFinancingLeaseObligationDerecognized_AE81A4D9052D11CAAE9AF008723922B5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_dbx_ImputedFinancingLeaseObligationDerecognized_AE81A4D9052D11CAAE9AF008723922B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_8B44BA852FBBCE8EDB9FF0087239B8BA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_8B44BA852FBBCE8EDB9FF0087239B8BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_5376AC61895940E7807FF0087239F467" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_5376AC61895940E7807FF0087239F467" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_2D393A64A4CB5742B810F008723A2533" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_D06100D52D4C4F8FBF5FF00872380084" xlink:to="loc_us-gaap_Depreciation_2D393A64A4CB5742B810F008723A2533" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/PropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1A79FEAADE825E11A3C9B6159F14CE27" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0984A52CA46858ECA97CC34FC67057BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1A79FEAADE825E11A3C9B6159F14CE27" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0984A52CA46858ECA97CC34FC67057BB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6F087FCE7F405049819DACAF2B0CC855" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0984A52CA46858ECA97CC34FC67057BB" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6F087FCE7F405049819DACAF2B0CC855" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_89AA4C82F380CB0C899A8F7B002868CF_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6F087FCE7F405049819DACAF2B0CC855" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_89AA4C82F380CB0C899A8F7B002868CF_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6F087FCE7F405049819DACAF2B0CC855" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BuildingMember" xlink:label="loc_us-gaap_BuildingMember_18FA37443BAF5FBD9C5CC964BDB72247" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:to="loc_us-gaap_BuildingMember_18FA37443BAF5FBD9C5CC964BDB72247" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember_80662AF1984A51FFBADA4EC352820C87" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:to="loc_us-gaap_ComputerEquipmentMember_80662AF1984A51FFBADA4EC352820C87" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_78347A8770C756C5870295D8839A47B8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_78347A8770C756C5870295D8839A47B8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_540BA42167C05B6AB9E8F38DEDFA34DF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_540BA42167C05B6AB9E8F38DEDFA34DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConstructionInProgressMember" xlink:label="loc_us-gaap_ConstructionInProgressMember_013B2294AFD15C78B6BC7D86B7CBCD71" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7657F9C0D7E052AD957AAF9795F86974" xlink:to="loc_us-gaap_ConstructionInProgressMember_013B2294AFD15C78B6BC7D86B7CBCD71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_87BE10772E085A14952BA2E17F9D991A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1A79FEAADE825E11A3C9B6159F14CE27" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_87BE10772E085A14952BA2E17F9D991A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2B76AEC58B535528935E09E42A5B9D47" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1A79FEAADE825E11A3C9B6159F14CE27" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_2B76AEC58B535528935E09E42A5B9D47" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_97EFE50A171C5E59BBF11AAD5CFE6F2D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_1A79FEAADE825E11A3C9B6159F14CE27" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_97EFE50A171C5E59BBF11AAD5CFE6F2D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/PropertyAndEquipmentNetTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/RelatedPartyTransactions" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_B26A5C80A2E45A6B933987E842B2A661" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_D50A3D0B557D51B58C60EC93DC70CFF4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B26A5C80A2E45A6B933987E842B2A661" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_D50A3D0B557D51B58C60EC93DC70CFF4" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9F57F7801A7D52E18E22D1F2F69C3BCE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_D50A3D0B557D51B58C60EC93DC70CFF4" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9F57F7801A7D52E18E22D1F2F69C3BCE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_ED11F596CB7E29299119C820FE25BB83_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9F57F7801A7D52E18E22D1F2F69C3BCE" xlink:to="loc_us-gaap_RelatedPartyDomain_ED11F596CB7E29299119C820FE25BB83_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaap_RelatedPartyDomain_F2371CF7ACB85665B1422B3928FDA1A9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_9F57F7801A7D52E18E22D1F2F69C3BCE" xlink:to="loc_us-gaap_RelatedPartyDomain_F2371CF7ACB85665B1422B3928FDA1A9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorityShareholderMember" xlink:label="loc_us-gaap_MajorityShareholderMember_639AEA4B0D1C57FD85277E6F367692EA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_F2371CF7ACB85665B1422B3928FDA1A9" xlink:to="loc_us-gaap_MajorityShareholderMember_639AEA4B0D1C57FD85277E6F367692EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AffiliatedEntityMember" xlink:label="loc_us-gaap_AffiliatedEntityMember_E22E864DD10C5CA884C1F3A55C2B4A7D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_F2371CF7ACB85665B1422B3928FDA1A9" xlink:to="loc_us-gaap_AffiliatedEntityMember_E22E864DD10C5CA884C1F3A55C2B4A7D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_D8B8BE51B6F65C828C4C86EF6368CA00" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_D50A3D0B557D51B58C60EC93DC70CFF4" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_D8B8BE51B6F65C828C4C86EF6368CA00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_54D27073F4E2E0613C8AC820FE265BF7_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_D8B8BE51B6F65C828C4C86EF6368CA00" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_54D27073F4E2E0613C8AC820FE265BF7_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_79DEB4EAD9E55ACD89BFECBACEC8E2E4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_D8B8BE51B6F65C828C4C86EF6368CA00" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_79DEB4EAD9E55ACD89BFECBACEC8E2E4" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_DropboxCharitableFoundationMember" xlink:label="loc_dbx_DropboxCharitableFoundationMember_B667724CECFD5C769F6EE7D8C16B0299" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_79DEB4EAD9E55ACD89BFECBACEC8E2E4" xlink:to="loc_dbx_DropboxCharitableFoundationMember_B667724CECFD5C769F6EE7D8C16B0299" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_InfrastructureEquipmentUnderCapitalLeasesAndCommercialProductsAndServicesMember" xlink:label="loc_dbx_InfrastructureEquipmentUnderCapitalLeasesAndCommercialProductsAndServicesMember_25A218D70794574F804E2F6AFD32E5A6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_79DEB4EAD9E55ACD89BFECBACEC8E2E4" xlink:to="loc_dbx_InfrastructureEquipmentUnderCapitalLeasesAndCommercialProductsAndServicesMember_25A218D70794574F804E2F6AFD32E5A6" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_RelatedPartyTransactionNumberOfControllingShareholders" xlink:label="loc_dbx_RelatedPartyTransactionNumberOfControllingShareholders_A617A1386D0051DD848C13ABD6C7E53D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B26A5C80A2E45A6B933987E842B2A661" xlink:to="loc_dbx_RelatedPartyTransactionNumberOfControllingShareholders_A617A1386D0051DD848C13ABD6C7E53D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_D2469164E8BD50F0A76DF67C52041127" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B26A5C80A2E45A6B933987E842B2A661" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_D2469164E8BD50F0A76DF67C52041127" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty" xlink:label="loc_us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty_671B9C3BFCF35CACA22115269EDF81E7" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_B26A5C80A2E45A6B933987E842B2A661" xlink:to="loc_us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty_671B9C3BFCF35CACA22115269EDF81E7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/RevolvingCreditFacility" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/RevolvingCreditFacilityDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_C22757B20C5951BE92DF9C19D5B6A229" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:to="loc_us-gaap_DebtInstrumentAxis_C22757B20C5951BE92DF9C19D5B6A229" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_B21A1B35C53489504D258F7AFFB745FF_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_C22757B20C5951BE92DF9C19D5B6A229" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_B21A1B35C53489504D258F7AFFB745FF_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2B4FD183C86658AC8748546AF8BE67D4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_C22757B20C5951BE92DF9C19D5B6A229" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2B4FD183C86658AC8748546AF8BE67D4" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CreditAndGuaranteeAgreementMember" xlink:label="loc_dbx_CreditAndGuaranteeAgreementMember_C93D909032E75DCBB66D23EFEA3B62EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_2B4FD183C86658AC8748546AF8BE67D4" xlink:to="loc_dbx_CreditAndGuaranteeAgreementMember_C93D909032E75DCBB66D23EFEA3B62EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_DB01DBFB0FF4548C88CD6F37E65F8878" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_DB01DBFB0FF4548C88CD6F37E65F8878" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_CB43FD0CB5A89086DF5E8F7AFFB7D5D2_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_DB01DBFB0FF4548C88CD6F37E65F8878" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_CB43FD0CB5A89086DF5E8F7AFFB7D5D2_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_A2372ECAED0F5667AC9DECDB3922D6FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_DB01DBFB0FF4548C88CD6F37E65F8878" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_A2372ECAED0F5667AC9DECDB3922D6FB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditMember" xlink:label="loc_us-gaap_LineOfCreditMember_DE2E1FD2FBDC531E9E4AF286AD60F606" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_A2372ECAED0F5667AC9DECDB3922D6FB" xlink:to="loc_us-gaap_LineOfCreditMember_DE2E1FD2FBDC531E9E4AF286AD60F606" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_A765A9F697BE5D559D3F1C028A88F9BA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:to="loc_us-gaap_CreditFacilityAxis_A765A9F697BE5D559D3F1C028A88F9BA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_509B7DD7EC7A05E472FA8F7AFFB8CFB2_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_A765A9F697BE5D559D3F1C028A88F9BA" xlink:to="loc_us-gaap_CreditFacilityDomain_509B7DD7EC7A05E472FA8F7AFFB8CFB2_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_38D154FAF96D5AE0B54C2C390C03F22D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_A765A9F697BE5D559D3F1C028A88F9BA" xlink:to="loc_us-gaap_CreditFacilityDomain_38D154FAF96D5AE0B54C2C390C03F22D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_233883886798560FBB8780810D45EDE3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_38D154FAF96D5AE0B54C2C390C03F22D" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_233883886798560FBB8780810D45EDE3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LetterOfCreditMember" xlink:label="loc_us-gaap_LetterOfCreditMember_282E067BAF4E5530AEE865C0A49FEC1A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_38D154FAF96D5AE0B54C2C390C03F22D" xlink:to="loc_us-gaap_LetterOfCreditMember_282E067BAF4E5530AEE865C0A49FEC1A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaap_VariableRateAxis_5CAAE82FEB7250E08DFDC770E383C766" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_823C812BE72D57C0826A4CCAEA7157ED" xlink:to="loc_us-gaap_VariableRateAxis_5CAAE82FEB7250E08DFDC770E383C766" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_E1A171EE82E2E55495128F7AFFB8EEA6_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_5CAAE82FEB7250E08DFDC770E383C766" xlink:to="loc_us-gaap_VariableRateDomain_E1A171EE82E2E55495128F7AFFB8EEA6_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaap_VariableRateDomain_96E70B5D718151F7AD1CD44B3524A98A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_5CAAE82FEB7250E08DFDC770E383C766" xlink:to="loc_us-gaap_VariableRateDomain_96E70B5D718151F7AD1CD44B3524A98A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_A44C96EA38A550279097D44E39638CE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_96E70B5D718151F7AD1CD44B3524A98A" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_A44C96EA38A550279097D44E39638CE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BaseRateMember" xlink:label="loc_us-gaap_BaseRateMember_0F1338B398925A99BD654270CE525221" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_96E70B5D718151F7AD1CD44B3524A98A" xlink:to="loc_us-gaap_BaseRateMember_0F1338B398925A99BD654270CE525221" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_6B91FDE59DAF580C80A047AC77B5E8F2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_6B91FDE59DAF580C80A047AC77B5E8F2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsGross" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsGross_35008D0A8EA0520F8903D331E0DF4E25" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsGross_35008D0A8EA0520F8903D331E0DF4E25" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentTerm" xlink:label="loc_us-gaap_DebtInstrumentTerm_4BD9FC3A4CA15D5E99EEFE3CE86D3A8E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_DebtInstrumentTerm_4BD9FC3A4CA15D5E99EEFE3CE86D3A8E" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_LineOfCreditFacilityAccordionFeatureIncreaseLimit" xlink:label="loc_dbx_LineOfCreditFacilityAccordionFeatureIncreaseLimit_BFDD7972B770534BA0E2BE5B33DAB5F4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_dbx_LineOfCreditFacilityAccordionFeatureIncreaseLimit_BFDD7972B770534BA0E2BE5B33DAB5F4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_99BA38D992185E4D9A801B212DA52377" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_99BA38D992185E4D9A801B212DA52377" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_2E54486DAA8C5781A9E14C1C96963E18" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_2E54486DAA8C5781A9E14C1C96963E18" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_LineOfCreditFacilityFrontingFeePercentage" xlink:label="loc_dbx_LineOfCreditFacilityFrontingFeePercentage_BFA78F68C19B52E2AD3E9CECCC678CB9" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_dbx_LineOfCreditFacilityFrontingFeePercentage_BFA78F68C19B52E2AD3E9CECCC678CB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_D2EE5DDF92E75CA399244EB80D24E4FD" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_D2EE5DDF92E75CA399244EB80D24E4FD" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_LineOfCreditFacilityCovenantTermsLiquidityRatioRequiredMinimum" xlink:label="loc_dbx_LineOfCreditFacilityCovenantTermsLiquidityRatioRequiredMinimum_E681DA5A95E6555E96094B6E17ECD3D1" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_dbx_LineOfCreditFacilityCovenantTermsLiquidityRatioRequiredMinimum_E681DA5A95E6555E96094B6E17ECD3D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_C769DA7DF28F52FCBED5893F4DAEA4F6" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_C769DA7DF28F52FCBED5893F4DAEA4F6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_25153A9B1C33507AB612E681D254E4AD" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_165CFF8E6BC2589FB14F6D758EA261E4" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_25153A9B1C33507AB612E681D254E4AD" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquity" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityCoFounderGrantsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_7247BE00491E0401F91CE206C2DD5957" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:to="loc_us-gaap_PlanNameAxis_7247BE00491E0401F91CE206C2DD5957" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_D93E3B97EB14C67A0EA0E206C2DD51B5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_7247BE00491E0401F91CE206C2DD5957" xlink:to="loc_us-gaap_PlanNameDomain_D93E3B97EB14C67A0EA0E206C2DD51B5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_D93E3B97EB14C67A0EA0E206C2DD51B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_7247BE00491E0401F91CE206C2DD5957" xlink:to="loc_us-gaap_PlanNameDomain_D93E3B97EB14C67A0EA0E206C2DD51B5" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CoFounderGrantsMember" xlink:label="loc_dbx_CoFounderGrantsMember_AE5238D37BBC7D7C9BF3E206C2DD3D8D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_D93E3B97EB14C67A0EA0E206C2DD51B5" xlink:to="loc_dbx_CoFounderGrantsMember_AE5238D37BBC7D7C9BF3E206C2DD3D8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_F1B2E581E8BF94228E26E206C2DE9A7F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:to="loc_us-gaap_TitleOfIndividualAxis_F1B2E581E8BF94228E26E206C2DE9A7F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_F1B2E581E8BF94228E26E206C2DE9A7F" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_F1B2E581E8BF94228E26E206C2DE9A7F" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ChiefExecutiveOfficerMember" xlink:label="loc_us-gaap_ChiefExecutiveOfficerMember_8F974F3C563B67B47DBFE206C2DE9522" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943" xlink:to="loc_us-gaap_ChiefExecutiveOfficerMember_8F974F3C563B67B47DBFE206C2DE9522" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DirectorMember" xlink:label="loc_us-gaap_DirectorMember_33694E803558F86F0210E206C2DF2E02" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_8660D8334D6C110407CAE206C2DE6943" xlink:to="loc_us-gaap_DirectorMember_33694E803558F86F0210E206C2DF2E02" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_4576C7768D0F88B0F58CE206C2DF104D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:to="loc_us-gaap_AwardTypeAxis_4576C7768D0F88B0F58CE206C2DF104D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F186F0E935CCDC93B6ACE206C2DF9714_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4576C7768D0F88B0F58CE206C2DF104D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F186F0E935CCDC93B6ACE206C2DF9714_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F186F0E935CCDC93B6ACE206C2DF9714" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4576C7768D0F88B0F58CE206C2DF104D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F186F0E935CCDC93B6ACE206C2DF9714" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_0586489EF016C4DDF658E206C2DF1CDC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_F186F0E935CCDC93B6ACE206C2DF9714" xlink:to="loc_us-gaap_RestrictedStockMember_0586489EF016C4DDF658E206C2DF1CDC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaap_VestingAxis_9CA3C46D6DD86EFF994DE206C2DF5424" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:to="loc_us-gaap_VestingAxis_9CA3C46D6DD86EFF994DE206C2DF5424" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_F2EC2B727842C6926E76E206C2E07EAA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_9CA3C46D6DD86EFF994DE206C2DF5424" xlink:to="loc_us-gaap_VestingDomain_F2EC2B727842C6926E76E206C2E07EAA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaap_VestingDomain_F2EC2B727842C6926E76E206C2E07EAA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_9CA3C46D6DD86EFF994DE206C2DF5424" xlink:to="loc_us-gaap_VestingDomain_F2EC2B727842C6926E76E206C2E07EAA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_1CE0BD8E739B41E23BA6E206C2E031E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_F2EC2B727842C6926E76E206C2E07EAA" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_1CE0BD8E739B41E23BA6E206C2E031E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_9CDD3361C04CE260E301E206C2E07C41" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_EAE02FFA16CEF0BC8B4AE206C2DDE4CA" xlink:to="loc_us-gaap_RangeAxis_9CDD3361C04CE260E301E206C2E07C41" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_9CDD3361C04CE260E301E206C2E07C41" xlink:to="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_9CDD3361C04CE260E301E206C2E07C41" xlink:to="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_6B11365CA14C4015BA64E206C2E1FE3E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8" xlink:to="loc_us-gaap_MinimumMember_6B11365CA14C4015BA64E206C2E1FE3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_B7A97BE12A4A3C6F46D6E206C2E1D63D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_5D8EDC82651037FCD78DE206C2E0DCD8" xlink:to="loc_us-gaap_MaximumMember_B7A97BE12A4A3C6F46D6E206C2E1D63D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_FBB0293BEFD9377EE764E206C2E14899" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_FBB0293BEFD9377EE764E206C2E14899" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_95B800AE513CEAD07BB8E206C2E13094" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_95B800AE513CEAD07BB8E206C2E13094" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches" xlink:label="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches_D561E47CE804C8DB6FBBE206C2E25CED" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_dbx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfTranches_D561E47CE804C8DB6FBBE206C2E25CED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_D0C949E404C18FF6258BE206C2E2598A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_D0C949E404C18FF6258BE206C2E2598A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_F3B0ECC26BEB82421343E206C2E2AAFB" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_F3B0ECC26BEB82421343E206C2E2AAFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_3133B58B97D53DBF2D08E206C2E234E5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_3133B58B97D53DBF2D08E206C2E234E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_E4265CA6BF27CF8265BCE206C2E22AB8" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_E4265CA6BF27CF8265BCE206C2E22AB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_26B59DE5F40916CF5C6BE206C2E38C56" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_26B59DE5F40916CF5C6BE206C2E38C56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_1276EB8D1B71FC590D68E206C2E3A2F0" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0FB7606606D03B639E37E206C2E1EF8B" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_1276EB8D1B71FC590D68E206C2E3A2F0" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityCommonStockConvertiblePreferredStockPreferredStockDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_520CA0828236AE0BD856E00086671D94" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:to="loc_us-gaap_StatementClassOfStockAxis_520CA0828236AE0BD856E00086671D94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_520CA0828236AE0BD856E00086671D94" xlink:to="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_520CA0828236AE0BD856E00086671D94" xlink:to="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_C4A6EBDC459632FBE82EE00086697ED5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:to="loc_us-gaap_CommonClassAMember_C4A6EBDC459632FBE82EE00086697ED5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_013FA159CD1E33BCEB43E000866A66FD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:to="loc_us-gaap_CommonClassBMember_013FA159CD1E33BCEB43E000866A66FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassCMember" xlink:label="loc_us-gaap_CommonClassCMember_30E91E10616CD6DF41C9E000866ADF0F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:to="loc_us-gaap_CommonClassCMember_30E91E10616CD6DF41C9E000866ADF0F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConvertiblePreferredStockMember" xlink:label="loc_us-gaap_ConvertiblePreferredStockMember_D955823CDB53CC04A13CE000866A3796" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_C66B7E821A66DDAB8057E000866771B2" xlink:to="loc_us-gaap_ConvertiblePreferredStockMember_D955823CDB53CC04A13CE000866A3796" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_993E565D518739B9CF1BE0008663B884" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:to="loc_us-gaap_PlanNameAxis_993E565D518739B9CF1BE0008663B884" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F006EE191285EF3B258AE00086648943_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_993E565D518739B9CF1BE0008663B884" xlink:to="loc_us-gaap_PlanNameDomain_F006EE191285EF3B258AE00086648943_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F006EE191285EF3B258AE00086648943" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_993E565D518739B9CF1BE0008663B884" xlink:to="loc_us-gaap_PlanNameDomain_F006EE191285EF3B258AE00086648943" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CoFounderGrantsMember" xlink:label="loc_dbx_CoFounderGrantsMember_232CEF340D6684D69E78E0008664368C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_F006EE191285EF3B258AE00086648943" xlink:to="loc_dbx_CoFounderGrantsMember_232CEF340D6684D69E78E0008664368C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_29432AF9ACB2137FB2EDE00086660361" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:to="loc_us-gaap_AwardTypeAxis_29432AF9ACB2137FB2EDE00086660361" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1284A0C84528DEAE8DFFE0008666C982_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_29432AF9ACB2137FB2EDE00086660361" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1284A0C84528DEAE8DFFE0008666C982_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1284A0C84528DEAE8DFFE0008666C982" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_29432AF9ACB2137FB2EDE00086660361" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1284A0C84528DEAE8DFFE0008666C982" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_0C73BE90420E80B7CCAAE0008666A386" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1284A0C84528DEAE8DFFE0008666C982" xlink:to="loc_us-gaap_RestrictedStockMember_0C73BE90420E80B7CCAAE0008666A386" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockByUniqueDescriptionAxis" xlink:label="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_55E83C7DA2E651A0DB32E00086642C3F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_354E796016AE1909E30FE0008663C8FE" xlink:to="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_55E83C7DA2E651A0DB32E00086642C3F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockNameDomain" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_55E83C7DA2E651A0DB32E00086642C3F" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockNameDomain" xlink:label="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConversionOfStockByUniqueDescriptionAxis_55E83C7DA2E651A0DB32E00086642C3F" xlink:to="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember" xlink:label="loc_dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember_993F246FCF5F5868EE57E0008665A532" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96" xlink:to="loc_dbx_ConversionOfConvertiblePreferredStockToClassBCommonStockMember_993F246FCF5F5868EE57E0008665A532" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember" xlink:label="loc_dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember_451B31C584D8367003C5E0008665F978" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConversionOfStockNameDomain_1FD134C5622B5AE37B10E00086656E96" xlink:to="loc_dbx_ConversionOfConvertiblePreferredStockToClassACommonStockMember_451B31C584D8367003C5E0008665F978" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_CommonStockVoteEquivalent" xlink:label="loc_dbx_CommonStockVoteEquivalent_4917FAAA004EFC45E47BE000866B9143" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_dbx_CommonStockVoteEquivalent_4917FAAA004EFC45E47BE000866B9143" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_00AE6EA89F255C273075E034F5EF18D9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_00AE6EA89F255C273075E034F5EF18D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_90ED96D3DEC63B71948AE000866CD8DA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_90ED96D3DEC63B71948AE000866CD8DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_84993D97F37F59A52612E000866B3D83" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_84993D97F37F59A52612E000866B3D83" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_631D82AEE85592699492E000866B7F60" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_CommonStockSharesIssued_631D82AEE85592699492E000866B7F60" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_C5DA1D3A6BACE4B70CA1E000866C5972" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_C5DA1D3A6BACE4B70CA1E000866C5972" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_930DCB337ACF75070095E000866C22C1" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_930DCB337ACF75070095E000866C22C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConversionOfStockSharesIssued1" xlink:label="loc_us-gaap_ConversionOfStockSharesIssued1_7D202D2E14E0CE875AEDE000866C9967" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_ConversionOfStockSharesIssued1_7D202D2E14E0CE875AEDE000866C9967" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_A74BE10E6FC5B36B4253E000866CA6B7" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_99A9D15D6793478344C9E000866BA1EB" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_A74BE10E6FC5B36B4253E000866CA6B7" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityEquityIncentivePlansDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_427058A7990F86925408E000865789C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_427058A7990F86925408E000865789C1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_A34D528095A40A0C3179E0008658D398" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_427058A7990F86925408E000865789C1" xlink:to="loc_us-gaap_PlanNameAxis_A34D528095A40A0C3179E0008658D398" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F8D33CFB4A4C05813C9BE0008659766A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_A34D528095A40A0C3179E0008658D398" xlink:to="loc_us-gaap_PlanNameDomain_F8D33CFB4A4C05813C9BE0008659766A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F8D33CFB4A4C05813C9BE0008659766A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_A34D528095A40A0C3179E0008658D398" xlink:to="loc_us-gaap_PlanNameDomain_F8D33CFB4A4C05813C9BE0008659766A" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_A2018PlanMember" xlink:label="loc_dbx_A2018PlanMember_9282B0C049F962A5BE8AE0008659F93B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_F8D33CFB4A4C05813C9BE0008659766A" xlink:to="loc_dbx_A2018PlanMember_9282B0C049F962A5BE8AE0008659F93B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_EE6F6B7321DB9C12B940E000865918C4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_427058A7990F86925408E000865789C1" xlink:to="loc_us-gaap_AwardTypeAxis_EE6F6B7321DB9C12B940E000865918C4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_027928A64D7FA02255A3E0008659D184_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_EE6F6B7321DB9C12B940E000865918C4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_027928A64D7FA02255A3E0008659D184_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_027928A64D7FA02255A3E0008659D184" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_EE6F6B7321DB9C12B940E000865918C4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_027928A64D7FA02255A3E0008659D184" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5B06C8CF60C3DDC6F1E9E000865A771B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_027928A64D7FA02255A3E0008659D184" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5B06C8CF60C3DDC6F1E9E000865A771B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_FBEDA9951E5FBFEB4ACFE00086577319" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_427058A7990F86925408E000865789C1" xlink:to="loc_us-gaap_StatementClassOfStockAxis_FBEDA9951E5FBFEB4ACFE00086577319" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_AC7BBEAA07910EA80EAAE0008658A129_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_FBEDA9951E5FBFEB4ACFE00086577319" xlink:to="loc_us-gaap_ClassOfStockDomain_AC7BBEAA07910EA80EAAE0008658A129_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_AC7BBEAA07910EA80EAAE0008658A129" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_FBEDA9951E5FBFEB4ACFE00086577319" xlink:to="loc_us-gaap_ClassOfStockDomain_AC7BBEAA07910EA80EAAE0008658A129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_060CEE801149A488469AE0008658EDFE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_AC7BBEAA07910EA80EAAE0008658A129" xlink:to="loc_us-gaap_CommonClassAMember_060CEE801149A488469AE0008658EDFE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_BB15B0B19BB1B3DF4CD6E000865A0859" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_BB15B0B19BB1B3DF4CD6E000865A0859" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_6310B5DA4786C55E0EBEE000865BFA75" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_6310B5DA4786C55E0EBEE000865BFA75" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_B5A243DA5FF1F677691AE000865B1BDF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_B5A243DA5FF1F677691AE000865B1BDF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_0542AB01A0566F2F304CE000865BAD1F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_0542AB01A0566F2F304CE000865BAD1F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_DFA894EB0BA8E72C30A5E000865B7249" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_DFA894EB0BA8E72C30A5E000865B7249" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_6C9B64BAB0019D616AA6E000865B4CEA" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_6C9B64BAB0019D616AA6E000865B4CEA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_A90CEF8F81D247BF7795E000865CC8D1" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_A90CEF8F81D247BF7795E000865CC8D1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_D30F2F41F251BF48389BE000865C3BDD" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_47698B0B45CDDD338B17E000865A69BC" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_D30F2F41F251BF48389BE000865C3BDD" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityScheduleOfPreTaxIntrinsicValueDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityScheduleOfStockOptionAndRestrictedStockActivityDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_CD093AA4034857D38D7CD643AE325060" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_CD093AA4034857D38D7CD643AE325060" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_9236D46D9E1B54E9946F81F7FAF58A38" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_CD093AA4034857D38D7CD643AE325060" xlink:to="loc_us-gaap_AwardTypeAxis_9236D46D9E1B54E9946F81F7FAF58A38" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8C91AD09BDCB23D212FD002E5DD1CC2A_43582933C8215117A73913397AD702AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9236D46D9E1B54E9946F81F7FAF58A38" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8C91AD09BDCB23D212FD002E5DD1CC2A_43582933C8215117A73913397AD702AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5F6B340FBA6651FBA07B85B0F3052A77" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9236D46D9E1B54E9946F81F7FAF58A38" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5F6B340FBA6651FBA07B85B0F3052A77" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_D427DA481CB65A5E9A53921262FF6DA8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5F6B340FBA6651FBA07B85B0F3052A77" xlink:to="loc_us-gaap_RestrictedStockMember_D427DA481CB65A5E9A53921262FF6DA8" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward" xlink:label="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_04AD636C1C045BF89983068C37ED2921" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_04AD636C1C045BF89983068C37ED2921" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_56D866B8BF2F5E69A7E45FE6C3C35D37" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_56D866B8BF2F5E69A7E45FE6C3C35D37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_9948D807CE3E59DB82CAFF6002FC52AD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_9948D807CE3E59DB82CAFF6002FC52AD" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesCanceled" xlink:label="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesCanceled_F5546636BDAB5F5AA9E512F15768EF1D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesCanceled_F5546636BDAB5F5AA9E512F15768EF1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_54CA7738A3EC55D0A41B97CCC9EC7DFF" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_54CA7738A3EC55D0A41B97CCC9EC7DFF" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_ShareBasedCompensationArrangementBySharebasedPaymentAwardDecreaseInNumberofSharesAuthorizedFromStockGranted" xlink:label="loc_dbx_ShareBasedCompensationArrangementBySharebasedPaymentAwardDecreaseInNumberofSharesAuthorizedFromStockGranted_165B34A9550A5AD2B3A65DCE72547348" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardSharesAvailableForIssuanceRollForward_67FE5E3B4CDB5829A1625D7A141F98AA" xlink:to="loc_dbx_ShareBasedCompensationArrangementBySharebasedPaymentAwardDecreaseInNumberofSharesAuthorizedFromStockGranted_165B34A9550A5AD2B3A65DCE72547348" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_56A093069E855035AF41C6E9DCDE2CDE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_56A093069E855035AF41C6E9DCDE2CDE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_158E43A53C795C58963E42848B72F9E1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_56A093069E855035AF41C6E9DCDE2CDE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_158E43A53C795C58963E42848B72F9E1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_B4CB7BE0547B58D7B6112A5397C386E6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_56A093069E855035AF41C6E9DCDE2CDE" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_B4CB7BE0547B58D7B6112A5397C386E6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_307FACB7D42459CB98DF3774D934597B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares_307FACB7D42459CB98DF3774D934597B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_B1272F3A6C6B5A4DAC9AA1552F69E996" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares_B1272F3A6C6B5A4DAC9AA1552F69E996" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_D47D7EA1859F5C799F8227BE13D63ECF" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_D47D7EA1859F5C799F8227BE13D63ECF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_92E44D8611C658D9A825C925D5C8C7C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_D47D7EA1859F5C799F8227BE13D63ECF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_92E44D8611C658D9A825C925D5C8C7C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_BD8646908B4F5A158E6CE5FFF78A5E2F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_D47D7EA1859F5C799F8227BE13D63ECF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_BD8646908B4F5A158E6CE5FFF78A5E2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_4F9A30367D045B0CBE9B0E7B1AF344EF" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_4F9A30367D045B0CBE9B0E7B1AF344EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_5155770ECE005FC68F45E70DD28C0F04" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_5155770ECE005FC68F45E70DD28C0F04" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_745EBE8BA948511DA86F33B081DC0B46" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_745EBE8BA948511DA86F33B081DC0B46" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_7398ABE6B84C55FA9F1CE85B408D187A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_745EBE8BA948511DA86F33B081DC0B46" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_7398ABE6B84C55FA9F1CE85B408D187A" xlink:type="arc" />
    <link:loc xlink:href="dbx-20180930.xsd#dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageRemainingContractualTerm" xlink:label="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageRemainingContractualTerm_CDD1F69AF0685FABBB60D9A7D9FDDA63" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_dbx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageRemainingContractualTerm_CDD1F69AF0685FABBB60D9A7D9FDDA63" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6E1D98CE6C0E5F4A9605A95C1BFB2FC2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6E1D98CE6C0E5F4A9605A95C1BFB2FC2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_AA3D998464E1545AAAB1A4D58AB57EAE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_AA3D998464E1545AAAB1A4D58AB57EAE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_F816235589EC56D286BB3BDC8C19D9AC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_F816235589EC56D286BB3BDC8C19D9AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8357A5FC095B5EBC9323B6077D27D7A4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_2F230F384C805E4AB53F2C8541224A8D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_8357A5FC095B5EBC9323B6077D27D7A4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1DF5E9CEC8185B6B9B5D557AA7AEF0B9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_C40CB8FF228154BC85B57FFA11F19D3A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_C40CB8FF228154BC85B57FFA11F19D3A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_AD6B6CB8862D5E86B1AD33C9773B8588" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_AD6B6CB8862D5E86B1AD33C9773B8588" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_A62D18C4828B5DDAB5D3B4297B7B4677" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_A62D18C4828B5DDAB5D3B4297B7B4677" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_7B5B4EBBFC645E64A67A2305792190EE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_ABD3AF5E2A4752BC82B91517B96249FE" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_7B5B4EBBFC645E64A67A2305792190EE" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.dropbox.com/role/StockholdersEquityTables" xlink:type="extended" />
</link:linkbase>
