AREA DE OPERACIÓN: MANIOBRAS EN VUELO a. Virajes escarpados

a) CoStar Realty Information, Inc., a Delaware corporation b) CoStar Limited, a U.K. company

c) CoStar UK Limited, a U.K. company

d) Grecam S.A.S., a France Societée par Actions Simplifiée e) Property and Portfolio Research, Inc., a Delaware corporation f) Property and Portfolio Research Ltd., a U.K. company g) Resolve Technology, Inc., a Delaware corporation h) VirtualPremise, Inc., a Delaware corporation i) LoopNet, Inc. a Delaware corporation j) REApplications, Inc., a Delaware corporation

k) CoStar Realty Information Canada Ltd., a British Columbia company l) CoStar International LLC., a Delaware company

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the following Registration Statements:

of our reports dated February 20, 2014, with respect to the consolidated financial statements and schedule of CoStar Group, Inc. and the effectiveness of internal control over financial reporting of CoStar Group, Inc. included in this Annual Report (Form 10-K) of CoStar Group, Inc. for the year ended December 31, 2013.

/s/ Ernst & Young LLP

McLean. Virginia February 20, 2014

(1 ) Registration Statement Number 333-82599 on Form S-8 pertaining to the Realty Information Group, Inc. 1998 Stock Incentive Plan,

(2 ) Registration Statement Number 333-92165 on Form S-8 pertaining to the CoStar Group, Inc. 1998 Stock Incentive Plan, as amended,

(3 ) Registration Statement Number 333-45770 on Form S-8 pertaining to the CoStar Group, Inc. 1998 Stock Incentive Plan, as amended,

(4 ) Registration Statement Number 333-69548 on Form S-8 pertaining to the CoStar Group, Inc. 1998 Stock Incentive Plan, as amended,

(5 ) Registration Statement Number 333-135709 on Form S-8 pertaining to the CoStar Group, Inc. Employee Stock Purchase Plan, (6 ) Registration Statement Number 333-143968 on Form S-8 pertaining to the CoStar Group, Inc. 2007 Stock Incentive Plan, as

amended,

(7 ) Registration Statement Number 333-167424 on Form S-8 pertaining to the CoStar Group, Inc. 2007 Stock Incentive Plan, as amended,

(8 ) Registration Statement Number 333-174407 on Form S-3 of CoStar Group, Inc., and

(9 ) Registration Statement Number 333-182377 on Form S-8 pertaining to the CoStar Group, Inc. 2007 Stock Incentive Plan, as amended;

CERTIFICATION

I, Andrew C. Florance, certify that:

1. I have reviewed this annual report on Form 10-K of CoStar Group, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report; 4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as

defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our

supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most

recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 20, 2014 By: /s/ Andrew C. Florance

Andrew C. Florance

Chief Executive Officer

CERTIFICATION

I, Brian J. Radecki, certify that:

1. I have reviewed this annual report on Form 10-K of CoStar Group, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report; 4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as

defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our

supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most

recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 20, 2014 By: /s/ Brian J. Radecki

Brian J. Radecki

Chief Financial Officer

CoStar Group, Inc. 1331 L Street, NW Washington, DC 20005

February 20, 2014 Securities and Exchange Commission

100 F Street, NE Washington, DC 20549

Re: Certification Of Principal Executive Officer Pursuant To 18 U.S.C. Sec. 1350 Dear Ladies and Gentlemen:

In connection with the accompanying Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , I, Andrew C. Florance, Chief Executive Officer of CoStar Group, Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

A signed original of this written statement required by Section 906, or other document authenticating, acknowledging or otherwise adopting the signature that appears in typed form within the electronic version of this written statement required by Section 906, has been provided to CoStar Group, Inc. and will be retained by CoStar Group, Inc. and furnished to the Securities and Exchange Commission or its staff upon request.

In accordance with Item 601 of Regulation S-K, this certification is being “furnished” as Exhibit 32.1 to CoStar Group, Inc.’s annual report and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

1) such Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C 78m or 78o (d)); and

2) the information contained in such Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , fairly presents, in all material respects, the financial condition and results of operations of CoStar Group, Inc.

By: /s/ Andrew C. Florance

Andrew C. Florance

Chief Executive Officer

CoStar Group, Inc. 1331 L Street, NW Washington, DC 20005

February 20, 2014 Securities and Exchange Commission

100 F Street, NE Washington, DC 20549

Re: Certification Of Principal Financial Officer Pursuant To 18 U.S.C. Sec. 1350 Dear Ladies and Gentlemen:

In connection with the accompanying Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , I, Brian J. Radecki, Chief Financial Officer of CoStar Group, Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

A signed original of this written statement required by Section 906, or other document authenticating, acknowledging or otherwise adopting the signature that appears in typed form within the electronic version of this written statement required by Section 906, has been provided to CoStar Group, Inc. and will be retained by CoStar Group, Inc. and furnished to the Securities and Exchange Commission or its staff upon request.

In accordance with Item 601 of Regulation S-K, this certification is being “furnished” as Exhibit 32.2 to CoStar Group, Inc.’s annual report and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act, except as expressly set forth by specific reference in such a filing.

1) such Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m or 78o (d)); and

2) the information contained in such Annual Report on Form 10-K of CoStar Group, Inc., for the year ended December 31, 2013 , fairly presents, in all material respects, the financial condition and results of operations of CoStar Group, Inc.

By: /s/ Brian J. Radecki

Brian J. Radecki

Chief Financial Officer

(Principal Financial and Accounting Officer and Duly Authorized