    <SEC-DOCUMENT>0001057352-19-000050-index.html : 20190424
    <SEC-HEADER>0001057352-19-000050.hdr.sgml : 20190424
    <ACCEPTANCE-DATETIME>20190423184744
    ACCESSION NUMBER:		0001057352-19-000050
    CONFORMED SUBMISSION TYPE:	DEFA14A
    PUBLIC DOCUMENT COUNT:		4
    FILED AS OF DATE:		20190424
    DATE AS OF CHANGE:		20190423
    EFFECTIVENESS DATE:		20190424

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			COSTAR GROUP INC
    		CENTRAL INDEX KEY:			0001057352
    		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-BUSINESS SERVICES, NEC [7389]
    		IRS NUMBER:				522091509
    		STATE OF INCORPORATION:			DE
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		DEFA14A
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	000-24531
    		FILM NUMBER:		19762366

    	BUSINESS ADDRESS:
    		STREET 1:		1331 L STREET NW
    		CITY:			WASHINGTON
    		STATE:			DC
    		ZIP:			20005
    		BUSINESS PHONE:		2023466500

    	MAIL ADDRESS:
    		STREET 1:		1331 L STREET NW
    		CITY:			WASHINGTON
    		STATE:			DC
    		ZIP:			20005
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>DEFA14A
    <SEQUENCE>1
    <FILENAME>a2019proxynoticesched14a1.htm
    <DESCRIPTION>DEFA14A
    <TEXT>
    Document 1 - file: a2019proxynoticesched14a1.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>2
    <FILENAME>notice1.jpg
    <TEXT>
    Document 2 - file: notice1.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>3
    <FILENAME>notice2.jpg
    <TEXT>
    Document 3 - file: notice2.jpg

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>4
    <FILENAME>notice3.jpg
    <TEXT>
    Document 4 - file: notice3.jpg

    </DOCUMENT>
    </SEC-DOCUMENT>