We
consent to the incorporation by reference in the following Registration
Statements of CoStar Group, Inc. and in the related Prospectuses:
(1) Registration
Statement Number 333-82599 on Form S-8
(2) Registration
Statement Number 333-92165 on Form S-8
(3) Registration
Statement Number 333-45770 on Form S-8
(4) Registration
Statement Number 333-69548 on Form S-8
(5) Registration
Statement Number 333-135709 on Form S-8
(6) Registration
Statement Number 333-143968 on Form S-8
of our
reports dated February 25, 2010, with respect to the consolidated financial
statements of CoStar Group, Inc., incorporated by reference in its Annual Report
(Form 10-K) for the year ended December 31, 2009, and the financial statement
schedule of CoStar Group, Inc., and the effectiveness of internal control over
financial reporting of CoStar Group, Inc included therein, filed with the
Securities and Exchange Commission.
/s/ Ernst
& Young LLP
McLean,
Virginia
February
25, 2010