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  <xsd:element id="csgp_AllowanceForDoubtfulAccountsAndBillingAdjustmentsTableTextBlock" name="AllowanceForDoubtfulAccountsAndBillingAdjustmentsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
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  <xsd:element id="csgp_AuctionRateSecuritiesVariableRateDebtInstrumentsInterestRateResetPeriod" name="AuctionRateSecuritiesVariableRateDebtInstrumentsInterestRateResetPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_AvailableForSaleShortTermInvestmentContractualMaturities" name="AvailableForSaleShortTermInvestmentContractualMaturities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_BuildingPhotographyMember" name="BuildingPhotographyMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_BusinessAcquisitionContingentConsiderationCashPayment" name="BusinessAcquisitionContingentConsiderationCashPayment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessAcquisitionDeferredConsiderationLiabilityReversal" name="BusinessAcquisitionDeferredConsiderationLiabilityReversal" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="csgp_BusinessAcquisitionPurchasePriceAllocationAcquiredCustomerBase" name="BusinessAcquisitionPurchasePriceAllocationAcquiredCustomerBase" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessAcquisitionPurchasePriceAllocationAcquiredDatabaseTechnology" name="BusinessAcquisitionPurchasePriceAllocationAcquiredDatabaseTechnology" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessAcquisitionPurchasePriceAllocationOtherAssetsAndLiabilities" name="BusinessAcquisitionPurchasePriceAllocationOtherAssetsAndLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessCombinationRecognizedGoodwillAcquired" name="BusinessCombinationRecognizedGoodwillAcquired" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDeferredTaxAssetsandLiabilitiesNet" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDeferredTaxAssetsandLiabilitiesNet" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_CivixMember" name="CivixMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_CorporateAllocation" name="CorporateAllocation" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_CorporateAllocationUs" name="CorporateAllocationUs" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CostarGroupInc2007StockIncentivePlanMember" name="CostarGroupInc2007StockIncentivePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
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  <xsd:element id="csgp_DebtInstrumentBasisSpreadOnVariableRateOneMonthInterestPeriod" name="DebtInstrumentBasisSpreadOnVariableRateOneMonthInterestPeriod" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_DebtInstrumentBasisSpreadOnVariableRatePerAnnum" name="DebtInstrumentBasisSpreadOnVariableRatePerAnnum" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_DebtIssuanceLegalFees" name="DebtIssuanceLegalFees" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_DebtIssuanceUnderwritingFees" name="DebtIssuanceUnderwritingFees" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_DefaultInterestRateSpreadPerAnnum" name="DefaultInterestRateSpreadPerAnnum" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_DeferredGainOnSaleOfBuildingNoncurrent" name="DeferredGainOnSaleOfBuildingNoncurrent" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_ExcessCashFlowPaymentMaturityPeriodWithinIssuanceOfFinancialStatements" name="ExcessCashFlowPaymentMaturityPeriodWithinIssuanceOfFinancialStatements" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_Exercisableatendofperiod" name="Exercisableatendofperiod" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_ExternalCustomersMember" name="ExternalCustomersMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_FairValueLiabilitiesDeferredConsiderationUponAcquisition" name="FairValueLiabilitiesDeferredConsiderationUponAcquisition" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
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  <xsd:element id="csgp_FirstExcessCashFlowRepaymentPercentage" name="FirstExcessCashFlowRepaymentPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
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  <xsd:element id="csgp_GrossUnrealizedGainsforAvailableForSaleSecurities" name="GrossUnrealizedGainsforAvailableForSaleSecurities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
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  <xsd:element id="csgp_Increaseinsharesofcommonstockissuedpursuanttostockplan" name="Increaseinsharesofcommonstockissuedpursuanttostockplan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_IntangiblesAndOtherAssetsAbstract" name="IntangiblesAndOtherAssetsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
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  <xsd:element abstract="true" id="csgp_IntersegmentRevenueMember" name="IntersegmentRevenueMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
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  <xsd:element abstract="true" id="csgp_LoopNetStockholdersMember" name="LoopNetStockholdersMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
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  <xsd:element id="csgp_MaximumDebtServiceCoverageRatio" name="MaximumDebtServiceCoverageRatio" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_MaximumOriginalMaturityOfHighlyLiquidInvestmentsToBeConsideredCashEquivalents" name="MaximumOriginalMaturityOfHighlyLiquidInvestmentsToBeConsideredCashEquivalents" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_MaximumTotalLeverageRatioAfterEightFiscalQuarters" name="MaximumTotalLeverageRatioAfterEightFiscalQuarters" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_MaximumTotalLeverageRatioForFifthThroughEighthQuartersAfterClosingDate" name="MaximumTotalLeverageRatioForFifthThroughEighthQuartersAfterClosingDate" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_MinimumContractualMaturitiesOnUnderlyingSecuritiesInvolvedInAuctionRateSecurities" name="MinimumContractualMaturitiesOnUnderlyingSecuritiesInvolvedInAuctionRateSecurities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_MinimumNumberOfCurrentLitigationMatters" name="MinimumNumberOfCurrentLitigationMatters" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_NumberOfConsecutiveQuartersToMantainCumulativeEbitdaRequiredForAwardSharesToVest" name="NumberOfConsecutiveQuartersToMantainCumulativeEbitdaRequiredForAwardSharesToVest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_NumberOfCustomersAccoutingForMoreThanFivePercentOfRevenue" name="NumberOfCustomersAccoutingForMoreThanFivePercentOfRevenue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_NumberOfDistinctIntangibleAsset" name="NumberOfDistinctIntangibleAsset" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
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  <xsd:element id="csgp_PercentageOfLoanAmortizationInYearOne" name="PercentageOfLoanAmortizationInYearOne" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_PercentageOfLoanAmortizationInYearThree" name="PercentageOfLoanAmortizationInYearThree" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_PercentageOfLoanAmortizationInYearTwo" name="PercentageOfLoanAmortizationInYearTwo" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_PercentageOfPurchasePriceOfCompanysCommonStockToMarketPrice" name="PercentageOfPurchasePriceOfCompanysCommonStockToMarketPrice" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
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  <xsd:element id="csgp_ProceedsFromExerciseOfStockOptionsAndEspp" name="ProceedsFromExerciseOfStockOptionsAndEspp" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock" name="PropertyPlantAndEquipmentEstimatedUsefulLivesTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ReactionWebMember" name="ReactionWebMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ReconciliationOfSegmentLiabilitiesToTotalLiabilitiesAbstract" name="ReconciliationOfSegmentLiabilitiesToTotalLiabilitiesAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_SecondExcessCashFlowRepaymentPercentage" name="SecondExcessCashFlowRepaymentPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_SecondExcessCashFlowRepaymentRequirement" name="SecondExcessCashFlowRepaymentRequirement" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_SegmentReportingSegmentGrossAssets" name="SegmentReportingSegmentGrossAssets" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_SharebasedCompensationSharesCanceledorExpiredUnderStockOptionPlansExercisePriceRange" name="SharebasedCompensationSharesCanceledorExpiredUnderStockOptionPlansExercisePriceRange" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_SharebasedCompensationSharesExercisedUnderStockOptionPlansExercisePriceRange" name="SharebasedCompensationSharesExercisedUnderStockOptionPlansExercisePriceRange" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_SharebasedCompensationSharesGrantedUnderStockOptionPlansExercisePriceRange" name="SharebasedCompensationSharesGrantedUnderStockOptionPlansExercisePriceRange" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_SharebasedCompensationSharesOutstandingUnderStockOptionPlansExercisePriceRange" name="SharebasedCompensationSharesOutstandingUnderStockOptionPlansExercisePriceRange" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_SharesAvailableEmployeeStockPurchasePlan" name="SharesAvailableEmployeeStockPurchasePlan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_ShortTermInvestmentsMaturityTerm" name="ShortTermInvestmentsMaturityTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_StockIncentivePlan1998Member" name="StockIncentivePlan1998Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_SubscriptionBasedLicensingAgreementMinimumTermYears" name="SubscriptionBasedLicensingAgreementMinimumTermYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_SummaryOfSignificantAccountingPoliciesLineItems" name="SummaryOfSignificantAccountingPoliciesLineItems" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_SummaryOfSignificantAccountingPoliciesTable" name="SummaryOfSignificantAccountingPoliciesTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_SwinglineLoanMember" name="SwinglineLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_TermOfConsentOrderPublicCommentPeriod" name="TermOfConsentOrderPublicCommentPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_ThirdExcessCashFlowRepaymentPercentage" name="ThirdExcessCashFlowRepaymentPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_ThirdExcessCashFlowRepaymentRequirement" name="ThirdExcessCashFlowRepaymentRequirement" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="csgp_TotalDeferredIncomeTaxPerYear" name="TotalDeferredIncomeTaxPerYear" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_TotalSegmentLiabilities" name="TotalSegmentLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_UnitedStatesMember" name="UnitedStatesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
</xsd:schema>
