Exhibit 10.23
February 4, 2010
Thomas L. Monahan, III
Chairman of the Board and Chief Executive Officer
The Corporate Executive Board Company
1919 North Lynn Street
Arlington, VA 22209

  Re:  
Collaboration Agreement, dated as of February 6, 2007, by and between The
Corporate Executive Board Company and The Advisory Board Company (the
“Collaboration Agreement”)

Dear Tom:
This letter confirms that The Corporate Executive Board Company (“CEB”) and The
Advisory Board Company (“ABCO”) have agreed to extend the Initial NP Term and
the Initial EC Term (as such terms are defined in the Collaboration Agreement)
through February 5, 2012 as contemplated by Sections 3.3(a) and 3.4(a) of the
Collaboration Agreement, respectively, effective as of February 4, 2010.
Please indicate your agreement with the foregoing by signing and returning one
copy of this letter to my attention, which shall constitute CEB’s and ABCO’s
agreement with respect to the subject matter hereof.

            Very truly yours,
      /s/ Robert W. Musslewhite       Robert W. Musslewhite      Chief Executive
Officer   

          ACCEPTED AND AGREED:    
 
        THE CORPORATE EXECUTIVE BOARD COMPANY    
 
       
By:
  /s/ Thomas L. Monahan, III    
 
 
 
Thomas L. Monahan, III    
 
  Chairman of the Board and Chief Executive Officer