<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001661073</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001057352</issuerCik>
            <issuerName>COSTAR GROUP INC.</issuerName>
            <secFileNumber>000-24531</secFileNumber>
            <issuerAddress>
                <ns2:street1>1331 L Street, NW</ns2:street1>
                <ns2:city>Washington</ns2:city>
                <ns2:stateOrCountry>DC</ns2:stateOrCountry>
                <ns2:zipCode>20005</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>(202) 346-6500</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>SCOTT WHEELER</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>24670</noOfUnitsSold>
            <aggregateMarketValue>1990481.68</aggregateMarketValue>
            <noOfUnitsOutstanding>408539209</noOfUnitsOutstanding>
            <approxSaleDate>06/12/2023</approxSaleDate>
            <securitiesExchangeName>NASD</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>02/28/2021</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>9490</amountOfSecuritiesAcquired>
            <paymentDate>02/28/2021</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>02/15/2021</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>15180</amountOfSecuritiesAcquired>
            <paymentDate>02/15/2021</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>06/12/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Scott T. Wheeler</signature>
        </noticeSignature>
    </formData>
</edgarSubmission>
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144
0001661073
XXXXXXXX
LIVE
0001057352
COSTAR GROUP INC.
000-24531
1331 L Street, NW
Washington
DC
20005
(202) 346-6500
SCOTT WHEELER
Officer
Common
Morgan Stanley Smith Barney LLC
1 New York Plaza
38th Floor
New York
NY
10004
24670
1990481.68
408539209
06/12/2023
NASD
Common
02/28/2021
Restricted Stock
Issuer
N
9490
02/28/2021
Not Applicable
Common
02/15/2021
Restricted Stock
Issuer
N
15180
02/15/2021
Not Applicable
Y
06/12/2023
/s/ Scott T. Wheeler