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                                                                   EXHIBIT 10.23


                                 PROMISSORY NOTE


$7,500,000                                                     December 21, 1999

        FOR VALUE RECEIVED, the undersigned, the Advisory Beard Company, a
Maryland corporation with its place of business at 600 New Hampshire Avenue,
N.W., Washington, D.C., 20037, promises to pay to order of David G. Bradley, an
individual with his principal residence at 2211 30th Street, N.W., Washington,
D.C., 20008, the principal sum of $7,500,000, with interest at the rate of seven
percent (7%) per annum, subject to the terms and conditions herein contained.

        1.      The principal sum shall be due and payable on December 21, 2000.

        2.      Interest on the outstanding balance of the principal sum shall
accrue at the rate of seven percent (7%) per annum from December 21, 1999 until
this Note is paid in full, and shall include an interim interest payment on July
1, 2000.

        3.      This Note may be prepaid in whole or in part at any time without
penalty.

        4.      This Note is secured by the cash, marketable securities, and
membership fees receivable of the Advisory Board Company.

        5.      Upon the occurrence of an Event of Default, as that term is
defined below, and the continuation of any such Event of Default for a period of
thirty days after the delivery of written notice to the undersigned setting
forth such Event of Default, the unpaid balance of the principal and any
interest accrued thereon shall, at the option of the holder hereof, at once
become due and payable. The notice of default shall be deemed to be delivered if
delivered to the undersigned or if sent by United States certified or registered
mail to the undersigned at the address set forth above or at the last address
furnished by it for such purpose.

        An Event of Default will be deemed to have occurred upon the happening
of any of the following events:

                (a)     Debtor fails to pay the principal payments and accrued
interest when due in accordance with the Note.

                (b)     Debtor files a voluntary proceeding under the Bankruptcy
Code, or any involuntary petitions under the Bankruptcy Code are filed against
the Debtor.

                (c)     Any lien or other attachment is placed against the
Collateral (other than the security interest created hereby) or a Writ of
Execution is served against the Collateral.

        6.      Any payment by the undersigned on this Note shall be credited
first to any interest then due, and the remainder on the principal sum, and
interest shall thereupon cease to accrue upon the amount so credited on the said
principal sum.




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        7.      All installments of principal and interest hereunder shall be
payable in lawful money of the United States.

IN WITNESS WHEREOF, the undersigned has set its hand and seal as of the day,
month and year first hereinabove written.

Debtor:
The Advisory Board Company, Inc.

/s/Jeffrey D. Zients                              12/21/99
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Jeffrey D. Zients, President                      Date



Creditor:
/s/David G. Bradley                               December 28, '99
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David G. Bradley                                  Date






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