<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<xsd:schema attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.costar.com/20181231" xmlns:csgp="http://www.costar.com/20181231" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:nonnum="http://www.xbrl.org/dtr/type/non-numeric" xmlns:num="http://www.xbrl.org/dtr/type/numeric" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:import namespace="http://fasb.org/srt/2018-01-31" schemaLocation="http://xbrl.fasb.org/srt/2018/elts/srt-2018-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-gaap/2018-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-gaap-2018-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-roles/2018-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-roles-2018-01-31.xsd" />
  <xsd:import namespace="http://fasb.org/us-types/2018-01-31" schemaLocation="http://xbrl.fasb.org/us-gaap/2018/elts/us-types-2018-01-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/arcrole/fact-explanatoryFact" schemaLocation="http://www.xbrl.org/lrr/arcrole/factExplanatory-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/negated" schemaLocation="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/2009/role/net" schemaLocation="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/non-numeric" schemaLocation="http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd" />
  <xsd:import namespace="http://www.xbrl.org/dtr/type/numeric" schemaLocation="http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd" />
  <xsd:import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/country/2017-01-31" schemaLocation="http://xbrl.sec.gov/country/2017/country-2017-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/currency/2017-01-31" schemaLocation="http://xbrl.sec.gov/currency/2017/currency-2017-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/dei/2018-01-31" schemaLocation="https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/exch/2018-01-31" schemaLocation="https://xbrl.sec.gov/exch/2018/exch-2018-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/invest/2013-01-31" schemaLocation="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/naics/2017-01-31" schemaLocation="http://xbrl.sec.gov/naics/2017/naics-2017-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/sic/2011-01-31" schemaLocation="http://xbrl.sec.gov/sic/2011/sic-2011-01-31.xsd" />
  <xsd:import namespace="http://xbrl.sec.gov/stpr/2018-01-31" schemaLocation="https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd" />
  <xsd:annotation>
    <xsd:appinfo>
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="csgp-20181231_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="csgp-20181231_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="csgp-20181231_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple" />
      <link:linkbaseRef xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="csgp-20181231_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple" />
      <link:roleType id="Acquisitions" roleURI="http://www.costar.com/role/Acquisitions">
        <link:definition>2110100 - Disclosure - ACQUISITIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsBusinessAcquisitionProFormaInformationDetails" roleURI="http://www.costar.com/role/AcquisitionsBusinessAcquisitionProFormaInformationDetails">
        <link:definition>2410405 - Disclosure - ACQUISITIONS (Business Acquisition, Pro Forma Information) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsForrentNarrativeDetails" roleURI="http://www.costar.com/role/AcquisitionsForrentNarrativeDetails">
        <link:definition>2410402 - Disclosure - ACQUISITIONS (ForRent Narrative) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsOtherNarrativeDetails" roleURI="http://www.costar.com/role/AcquisitionsOtherNarrativeDetails">
        <link:definition>2410404 - Disclosure - ACQUISITIONS (Other - Narrative) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsScheduleOfRecognizedIdentifiedAssetsAcquiredAndLiabilitiesAssumedDetails" roleURI="http://www.costar.com/role/AcquisitionsScheduleOfRecognizedIdentifiedAssetsAcquiredAndLiabilitiesAssumedDetails">
        <link:definition>2410403 - Disclosure - ACQUISITIONS (Schedule of Recognized Identified Assets Acquired and Liabilities Assumed) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="AcquisitionsTables" roleURI="http://www.costar.com/role/AcquisitionsTables">
        <link:definition>2310301 - Disclosure - ACQUISITIONS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsAndContingencies" roleURI="http://www.costar.com/role/CommitmentsAndContingencies">
        <link:definition>2118100 - Disclosure - COMMITMENTS AND CONTINGENCIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsAndContingenciesDetails" roleURI="http://www.costar.com/role/CommitmentsAndContingenciesDetails">
        <link:definition>2418402 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsAndContingenciesTables" roleURI="http://www.costar.com/role/CommitmentsAndContingenciesTables">
        <link:definition>2318301 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedBalanceSheets" roleURI="http://www.costar.com/role/ConsolidatedBalanceSheets">
        <link:definition>1004000 - Statement - CONSOLIDATED BALANCE SHEETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedBalanceSheetsParenthetical" roleURI="http://www.costar.com/role/ConsolidatedBalanceSheetsParenthetical">
        <link:definition>1004501 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsOfCashFlows" roleURI="http://www.costar.com/role/ConsolidatedStatementsOfCashFlows">
        <link:definition>1006000 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsOfComprehensiveIncomeLoss" roleURI="http://www.costar.com/role/ConsolidatedStatementsOfComprehensiveIncomeLoss">
        <link:definition>1003000 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsOfOperations" roleURI="http://www.costar.com/role/ConsolidatedStatementsOfOperations">
        <link:definition>1002000 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ConsolidatedStatementsOfStockholdersEquity" roleURI="http://www.costar.com/role/ConsolidatedStatementsOfStockholdersEquity">
        <link:definition>1005000 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DocumentAndEntityInformation" roleURI="http://www.costar.com/role/DocumentAndEntityInformation">
        <link:definition>0001000 - Document - DOCUMENT AND ENTITY INFORMATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlans" roleURI="http://www.costar.com/role/EmployeeBenefitPlans">
        <link:definition>2122100 - Disclosure - EMPLOYEE BENEFIT PLANS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansAssumptionsDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansAssumptionsDetails">
        <link:definition>2422404 - Disclosure - EMPLOYEE BENEFIT PLANS (Assumptions) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansEmployee401KPlanEmployeePensionPlanRegisteredRetirementSavingsPlanAndEmployeeStockPurchasePlanDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansEmployee401KPlanEmployeePensionPlanRegisteredRetirementSavingsPlanAndEmployeeStockPurchasePlanDetails">
        <link:definition>2422408 - Disclosure - EMPLOYEE BENEFIT PLANS (Employee 401(k) Plan, Employee Pension Plan, Registered Retirement Savings Plan and Employee Stock Purchase Plan) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansInformationRegardingStockOptionsDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansInformationRegardingStockOptionsDetails">
        <link:definition>2422405 - Disclosure - EMPLOYEE BENEFIT PLANS (Information Regarding Stock Options) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansRestrictiveStockAwardActivityDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansRestrictiveStockAwardActivityDetails">
        <link:definition>2422406 - Disclosure - EMPLOYEE BENEFIT PLANS (Restrictive Stock Award Activity) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansRestrictiveStockUnitsDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansRestrictiveStockUnitsDetails">
        <link:definition>2422407 - Disclosure - EMPLOYEE BENEFIT PLANS (Restrictive Stock Units) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansStockIncenticePlansNarrativeDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansStockIncenticePlansNarrativeDetails">
        <link:definition>2422402 - Disclosure - EMPLOYEE BENEFIT PLANS (Stock Incentice Plans - Narrative) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansStockOptionActivityDetails" roleURI="http://www.costar.com/role/EmployeeBenefitPlansStockOptionActivityDetails">
        <link:definition>2422403 - Disclosure - EMPLOYEE BENEFIT PLANS (Stock Option Activity) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="EmployeeBenefitPlansTables" roleURI="http://www.costar.com/role/EmployeeBenefitPlansTables">
        <link:definition>2322301 - Disclosure - EMPLOYEE BENEFIT PLANS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValue" roleURI="http://www.costar.com/role/FairValue">
        <link:definition>2112100 - Disclosure - FAIR VALUE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueDetails" roleURI="http://www.costar.com/role/FairValueDetails">
        <link:definition>2412402 - Disclosure - FAIR VALUE (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueTables" roleURI="http://www.costar.com/role/FairValueTables">
        <link:definition>2312301 - Disclosure - FAIR VALUE (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Goodwill" roleURI="http://www.costar.com/role/Goodwill">
        <link:definition>2114100 - Disclosure - GOODWILL</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillGoodwillBySegmentDetails" roleURI="http://www.costar.com/role/GoodwillGoodwillBySegmentDetails">
        <link:definition>2414402 - Disclosure - GOODWILL (Goodwill by Segment) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillNarrativeDetails" roleURI="http://www.costar.com/role/GoodwillNarrativeDetails">
        <link:definition>2414403 - Disclosure - GOODWILL (Narrative) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="GoodwillTables" roleURI="http://www.costar.com/role/GoodwillTables">
        <link:definition>2314301 - Disclosure - GOODWILL (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxes" roleURI="http://www.costar.com/role/IncomeTaxes">
        <link:definition>2117100 - Disclosure - INCOME TAXES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesComponentsForProvisionForIncomeTaxesDetails" roleURI="http://www.costar.com/role/IncomeTaxesComponentsForProvisionForIncomeTaxesDetails">
        <link:definition>2417402 - Disclosure - INCOME TAXES (Components for Provision for Income Taxes) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesComponentsOfDeferredTaxAssetsAndLiabilitiesDetails" roleURI="http://www.costar.com/role/IncomeTaxesComponentsOfDeferredTaxAssetsAndLiabilitiesDetails">
        <link:definition>2417403 - Disclosure - INCOME TAXES (Components of Deferred Tax Assets and Liabilities) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesNarrativeDetails" roleURI="http://www.costar.com/role/IncomeTaxesNarrativeDetails">
        <link:definition>2417405 - Disclosure - INCOME TAXES (Narrative) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesReconciliationOfProvisionForIncomeTaxesDetails" roleURI="http://www.costar.com/role/IncomeTaxesReconciliationOfProvisionForIncomeTaxesDetails">
        <link:definition>2417404 - Disclosure - INCOME TAXES (Reconciliation of Provision for Income Taxes) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesTables" roleURI="http://www.costar.com/role/IncomeTaxesTables">
        <link:definition>2317301 - Disclosure - INCOME TAXES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IncomeTaxesUnrecognizedTaxBenefitsDetails" roleURI="http://www.costar.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails">
        <link:definition>2417406 - Disclosure - INCOME TAXES (Unrecognized Tax Benefits) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssets" roleURI="http://www.costar.com/role/IntangibleAssets">
        <link:definition>2115100 - Disclosure - INTANGIBLE ASSETS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsDetails" roleURI="http://www.costar.com/role/IntangibleAssetsDetails">
        <link:definition>2415402 - Disclosure - INTANGIBLE ASSETS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="IntangibleAssetsTables" roleURI="http://www.costar.com/role/IntangibleAssetsTables">
        <link:definition>2315301 - Disclosure - INTANGIBLE ASSETS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Investments" roleURI="http://www.costar.com/role/Investments">
        <link:definition>2111100 - Disclosure - INVESTMENTS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InvestmentsAvailableForSaleSecuritiesDetails" roleURI="http://www.costar.com/role/InvestmentsAvailableForSaleSecuritiesDetails">
        <link:definition>2411403 - Disclosure - INVESTMENTS (Available For Sale Securities) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InvestmentsScheduledMaturitiesOfInvestmentsClassifiedAsAvailableForSaleDetails" roleURI="http://www.costar.com/role/InvestmentsScheduledMaturitiesOfInvestmentsClassifiedAsAvailableForSaleDetails">
        <link:definition>2411402 - Disclosure - INVESTMENTS (Scheduled Maturities of Investments Classified as Available-for-sale) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="InvestmentsTables" roleURI="http://www.costar.com/role/InvestmentsTables">
        <link:definition>2311301 - Disclosure - INVESTMENTS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebt" roleURI="http://www.costar.com/role/LongTermDebt">
        <link:definition>2116100 - Disclosure - LONG-TERM DEBT</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="LongTermDebtDetails" roleURI="http://www.costar.com/role/LongTermDebtDetails">
        <link:definition>2416401 - Disclosure - LONG-TERM DEBT (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetIncomeLossPerShareDetails" roleURI="http://www.costar.com/role/NetIncomeLossPerShareDetails">
        <link:definition>2421402 - Disclosure - NET INCOME (LOSS) PER SHARE (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetIncomeLossPerShareTables" roleURI="http://www.costar.com/role/NetIncomeLossPerShareTables">
        <link:definition>2321301 - Disclosure - NET INCOME (LOSS) PER SHARE (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="NetIncomePerShare" roleURI="http://www.costar.com/role/NetIncomePerShare">
        <link:definition>2121100 - Disclosure - NET INCOME PER SHARE</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="Organization" roleURI="http://www.costar.com/role/Organization">
        <link:definition>2107100 - Disclosure - ORGANIZATION</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="OrganizationDetails" roleURI="http://www.costar.com/role/OrganizationDetails">
        <link:definition>2407401 - Disclosure - ORGANIZATION (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyAndEquipment" roleURI="http://www.costar.com/role/PropertyAndEquipment">
        <link:definition>2113100 - Disclosure - PROPERTY AND EQUIPMENT</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyAndEquipmentDetails" roleURI="http://www.costar.com/role/PropertyAndEquipmentDetails">
        <link:definition>2413402 - Disclosure - PROPERTY AND EQUIPMENT (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="PropertyAndEquipmentTables" roleURI="http://www.costar.com/role/PropertyAndEquipmentTables">
        <link:definition>2313301 - Disclosure - PROPERTY AND EQUIPMENT (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="QuarterlyResultsOfOperations" roleURI="http://www.costar.com/role/QuarterlyResultsOfOperations">
        <link:definition>2123100 - Disclosure - QUARTERLY RESULTS OF OPERATIONS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="QuarterlyResultsOfOperationsDetails" roleURI="http://www.costar.com/role/QuarterlyResultsOfOperationsDetails">
        <link:definition>2423402 - Disclosure - QUARTERLY RESULTS OF OPERATIONS (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="QuarterlyResultsOfOperationsTables" roleURI="http://www.costar.com/role/QuarterlyResultsOfOperationsTables">
        <link:definition>2323301 - Disclosure - QUARTERLY RESULTS OF OPERATIONS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomers" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomers">
        <link:definition>2109100 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersCommissionsDetails" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersCommissionsDetails">
        <link:definition>2409405 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Commissions) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersContractAssetsAndLiabilitiesDetails" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersContractAssetsAndLiabilitiesDetails">
        <link:definition>2409403 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Contract Assets and Liabilities) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersContractAssetsDetails" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersContractAssetsDetails">
        <link:definition>2409404 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Contract Assets) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersDisaggregatedRevenueDetails" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersDisaggregatedRevenueDetails">
        <link:definition>2409402 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Disaggregated Revenue) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersPerformanceObligationsDetails" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersPerformanceObligationsDetails">
        <link:definition>2409406 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Performance Obligations) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="RevenueFromContractsWithCustomersTables" roleURI="http://www.costar.com/role/RevenueFromContractsWithCustomersTables">
        <link:definition>2309301 - Disclosure - REVENUE FROM CONTRACTS WITH CUSTOMERS (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ScheduleIiValuationAndQualifyingAccounts" roleURI="http://www.costar.com/role/ScheduleIiValuationAndQualifyingAccounts">
        <link:definition>2126100 - Disclosure - Schedule II Valuation and Qualifying Accounts</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ScheduleIiValuationAndQualifyingAccountsDetails" roleURI="http://www.costar.com/role/ScheduleIiValuationAndQualifyingAccountsDetails">
        <link:definition>2426401 - Disclosure - Schedule II Valuation and Qualifying Accounts (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentReporting" roleURI="http://www.costar.com/role/SegmentReporting">
        <link:definition>2119100 - Disclosure - SEGMENT REPORTING</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentReportingAssetsAndLiabilitiesDetails" roleURI="http://www.costar.com/role/SegmentReportingAssetsAndLiabilitiesDetails">
        <link:definition>2419403 - Disclosure - SEGMENT REPORTING (Assets and Liabilities) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentReportingReconciliationOfNetIncomeLossToEbitdaDetails" roleURI="http://www.costar.com/role/SegmentReportingReconciliationOfNetIncomeLossToEbitdaDetails">
        <link:definition>2419402 - Disclosure - SEGMENT REPORTING (Reconciliation of Net Income (Loss) to EBITDA) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SegmentReportingTables" roleURI="http://www.costar.com/role/SegmentReportingTables">
        <link:definition>2319301 - Disclosure - SEGMENT REPORTING (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockholdersEquity" roleURI="http://www.costar.com/role/StockholdersEquity">
        <link:definition>2120100 - Disclosure - STOCKHOLDERS' EQUITY</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StockholdersEquityDetails" roleURI="http://www.costar.com/role/StockholdersEquityDetails">
        <link:definition>2420401 - Disclosure - STOCKHOLDERS' EQUITY (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPolicies" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPolicies">
        <link:definition>2108100 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesDebtIssuanceCostsDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesDebtIssuanceCostsDetails">
        <link:definition>2408409 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Debt Issuance Costs) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesEffectOfNewAccountingChangeDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesEffectOfNewAccountingChangeDetails">
        <link:definition>2408411 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Effect of New Accounting Change) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesForeignCurrencyTranslationAndAccumulatedOtherComprehensiveLossDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesForeignCurrencyTranslationAndAccumulatedOtherComprehensiveLossDetails">
        <link:definition>2408404 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Foreign Currency Translation and Accumulated Other Comprehensive Loss) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesGoodwillAndIntangibleAssetsDetails">
        <link:definition>2408408 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Goodwill and Intangible Assets) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesImpactOfAdoptionsDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesImpactOfAdoptionsDetails">
        <link:definition>2408412 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Impact of Adoptions) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesPolicies" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesPolicies">
        <link:definition>2208201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails">
        <link:definition>2408407 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Property and Equipment) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesRecentAccountingPronouncementsDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesRecentAccountingPronouncementsDetails">
        <link:definition>2408410 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Recent Accounting Pronouncements) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesRevenueRecognitionAndAdvertisingCostsDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesRevenueRecognitionAndAdvertisingCostsDetails">
        <link:definition>2408403 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Revenue Recognition and Advertising Costs) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesStockBasedCompensationDetails">
        <link:definition>2408405 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Stock-Based Compensation) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryOfSignificantAccountingPoliciesTables" roleURI="http://www.costar.com/role/SummaryOfSignificantAccountingPoliciesTables">
        <link:definition>2308302 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xsd:appinfo>
  </xsd:annotation>
  <xsd:element abstract="true" id="csgp_A2017CreditAgreementMember" name="A2017CreditAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_AmortizationOfIntangibleAssetsCostofRevenue" name="AmortizationOfIntangibleAssetsCostofRevenue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_AmortizationOfIntangibleAssetsNetOfAdjustments" name="AmortizationOfIntangibleAssetsNetOfAdjustments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_AuctionRateSecuritiesVariableRateDebtInstrumentsInterestRateResetPeriod" name="AuctionRateSecuritiesVariableRateDebtInstrumentsInterestRateResetPeriod" 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_BusinessCombinationEmployeeBonusCompensationforRetention" name="BusinessCombinationEmployeeBonusCompensationforRetention" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedIndemnificationAsset" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedIndemnificationAsset" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedOtherAssetsAndLiabilities" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedOtherAssetsAndLiabilities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="csgp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedStateUncertainIncomeTaxPositionLiability" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedStateUncertainIncomeTaxPositionLiability" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_ChangeinContractwithCustomerLiabilityRollForward" name="ChangeinContractwithCustomerLiabilityRollForward" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CoStarGroupInc.2016StockIncentivePlanMember" name="CoStarGroupInc.2016StockIncentivePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CoStarSuiteMember" name="CoStarSuiteMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CommercialpropertyandlandMember" name="CommercialpropertyandlandMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_ContractwithCustomerAssetAdoptionofNewAccountingPrinciple" name="ContractwithCustomerAssetAdoptionofNewAccountingPrinciple" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="csgp_ContractwithCustomerAssetEffectsofCurrencyTranslation" name="ContractwithCustomerAssetEffectsofCurrencyTranslation" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_ContractwithCustomerLiabilityNewDeferralsNetofAmountsRecognizedinCurrentPeriod" name="ContractwithCustomerLiabilityNewDeferralsNetofAmountsRecognizedinCurrentPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CostarGroupInc2007StockIncentivePlanMember" name="CostarGroupInc2007StockIncentivePlanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_CozyServicesLtdMember" name="CozyServicesLtdMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_DecreaseinRevenue" name="DecreaseinRevenue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_DeferredTaxLiabilitiesAccruedCommissions" name="DeferredTaxLiabilitiesAccruedCommissions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="csgp_Deferredgainonthesaleofbuildingcurrent" name="Deferredgainonthesaleofbuildingcurrent" 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 id="csgp_EffectiveIncomeTaxRateReconciliationChangeInTaxReservesAmount" name="EffectiveIncomeTaxRateReconciliationChangeInTaxReservesAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_EffectiveIncomeTaxRateReconciliationExcessTaxBenefitAmount" name="EffectiveIncomeTaxRateReconciliationExcessTaxBenefitAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" 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_Exercisableatendofperiod" name="Exercisableatendofperiod" nillable="true" substitutionGroup="xbrli:item" type="num:perShareItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_ExerciseRange1Member" name="ExerciseRange1Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange2Member" name="ExerciseRange2Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange3Member" name="ExerciseRange3Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange4Member" name="ExerciseRange4Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange5Member" name="ExerciseRange5Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange6Member" name="ExerciseRange6Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange7Member" name="ExerciseRange7Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ExerciseRange9Member" name="ExerciseRange9Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_FederalFundsRateMember" name="FederalFundsRateMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ForRentDivisionOfDEHoldingsInc.Member" name="ForRentDivisionOfDEHoldingsInc.Member" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_GoodwillAbstract" name="GoodwillAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_IncomeTaxPenaltiesandInterestExpenseReversal" name="IncomeTaxPenaltiesandInterestExpenseReversal" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="csgp_IncreaseDecreaseDeferredCommissions" name="IncreaseDecreaseDeferredCommissions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="csgp_Increaseinsharesofcommonstockissuedpursuanttostockplan" name="Increaseinsharesofcommonstockissuedpursuanttostockplan" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_InformationAndAnalyticsMember" name="InformationAndAnalyticsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_InformationservicesMember" name="InformationservicesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_InitialBasisSpreadMember" name="InitialBasisSpreadMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_InitialBasisSpreadOneMonthLIBORMember" name="InitialBasisSpreadOneMonthLIBORMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_InitialPaymentstoAcquireBusinessesNetofCashAcquired" name="InitialPaymentstoAcquireBusinessesNetofCashAcquired" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_InternationalMember" name="InternationalMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_InvestmentOwnedShares" name="InvestmentOwnedShares" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_LandWatchMember" name="LandWatchMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_LineOfCreditFacilityCovenantComplianceSecuredLeverageRatio" name="LineOfCreditFacilityCovenantComplianceSecuredLeverageRatio" nillable="true" substitutionGroup="xbrli:item" type="xbrli:pureItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_LineOfCreditFacilityCovenantComplianceTotalLeverageRatio" name="LineOfCreditFacilityCovenantComplianceTotalLeverageRatio" nillable="true" substitutionGroup="xbrli:item" type="xbrli:pureItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_MinimumContractualMaturitiesOnUnderlyingSecuritiesInvolvedInAuctionRateSecurities" name="MinimumContractualMaturitiesOnUnderlyingSecuritiesInvolvedInAuctionRateSecurities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_MultifamilyOnlineMarketplaceMember" name="MultifamilyOnlineMarketplaceMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_NetincomelossbeforeinterestandotherincomeexpenseincometaxesdepreciationandamortizationEBITDA" name="NetincomelossbeforeinterestandotherincomeexpenseincometaxesdepreciationandamortizationEBITDA" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="csgp_NoncashorPartNoncashAcquisitionConsiderationOwedforAcquisitions" name="NoncashorPartNoncashAcquisitionConsiderationOwedforAcquisitions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_OnlineMarketplacesMember" name="OnlineMarketplacesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_OptionsExercisableAbstract" name="OptionsExercisableAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_PercentageOfPurchasePriceOfCompanysCommonStockToMarketPrice" name="PercentageOfPurchasePriceOfCompanysCommonStockToMarketPrice" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_PerformanceBasedRSAsWithoutMarketConditionMember" name="PerformanceBasedRSAsWithoutMarketConditionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_PerformancebasedRSAswithMarketConditionMember" name="PerformancebasedRSAswithMarketConditionMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <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_RealizedTaxBenefitsRelatedToOperatingLossCarryforward" name="RealizedTaxBenefitsRelatedToOperatingLossCarryforward" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="csgp_ReallaLtdMember" name="ReallaLtdMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="csgp_ScheduleofCommissionsExpenseTableTextBlock" name="ScheduleofCommissionsExpenseTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_ShareBasedCompensationExercisableRangeAbstract" name="ShareBasedCompensationExercisableRangeAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <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_SubscriptionBasedLicensingAgreementMinimumTermYears" name="SubscriptionBasedLicensingAgreementMinimumTermYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_TheScreeningProsLLCMember" name="TheScreeningProsLLCMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_VariableRateComponentAxis" name="VariableRateComponentAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_VariableRateComponentDomain" name="VariableRateComponentDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="csgp_WestsideRentalsMember" name="WestsideRentalsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
</xsd:schema>
