Exhibit 99(a)

JOINT FILING AGREEMENT

The undersigned hereby agree that the Schedule 13G with respect to the Common shares of beneficial interest, $.01 par value per share, of Government Properties Income Trust, dated as of January 26, 2010, is, and any amendments thereto (including amendments on Schedule 13D) signed by each of the undersigned shall be, filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended.

January 26, 2010

(Date)

HRPT PROPERTIES TRUST

/s/ John Popeo

(Signature)

John Popeo, Treasurer and Chief Financial Officer

(Name/Title)

REIT MANAGEMENT & RESEARCH LLC

/s/ Adam D. Portnoy

(Signature)

Adam D. Portnoy, President and Chief Executive Officer

(Name/Title)

REIT MANAGEMENT & RESEARCH TRUST

/s/ Adam D. Portnoy

(Signature)

Adam D. Portnoy, President and Chief Executive Officer

(Name/Title)

BARRY M. PORTNOY

/s/ Barry M. Portnoy

(Signature)

ADAM D. PORTNOY

/s/ Adam D. Portnoy

(Signature)