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                                                                   EXHIBIT 10.10

                              EMPLOYMENT AGREEMENT

     THIS AGREEMENT (the "AGREEMENT") is made as of the 29th day of November,
2002 (the "EFFECTIVE DATE"), by and between Bryan J. Koop (the "EMPLOYEE") and
Boston Properties, Inc., a Delaware corporation, with its principal executive
office located at 111 Huntington Avenue, Suite 300, Boston, Massachusetts
02199-7610 (together with its subsidiaries, the "COMPANY").

                                WITNESSETH THAT:

     WHEREAS, the Company has determined that it is in its best interest to
continue the employment of the Employee on the terms hereinafter set forth;

     WHEREAS, the Employee wishes to be so employed pursuant to the terms
hereinafter set forth;

     WHEREAS, the Company has adopted that certain Senior Executive Severance
Plan, effective as of July 30, 1998 (the "SEVERANCE PLAN"), as may be amended
from time to time, and which the parties desire to remain in full force and
effect after the date hereof;

     NOW, THEREFORE, in consideration of the mutual covenants and premises set
forth herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Company and the Employee
hereby agree as follows:

     1.  TERM. Subject to the provisions of Paragraph 8, the term of employment
pursuant to this Agreement (the "TERM") shall be two (2) years from the
Effective Date and shall be renewed automatically for periods of one (1) year
commencing at each anniversary of the Effective Date, unless written notice is
given by either party to the other not less than ninety (90) days prior to any
such anniversary of such party's election not to extend the Term.

     2.  EMPLOYMENT; DUTIES; LOCATION.

         (a) Employee shall initially serve as an officer of the Company with
the title Senior Vice President, Regional Manager. Employee's duties and
authority shall be commensurate with his title and position with the Company.
The Employee shall report directly to the Executive Vice President for Operation
and shall serve the Company in such other capacity or capacities as the Employee
may be requested to serve by the Board of Directors of the Company (the "BOARD
OF DIRECTORS"). In such capacity or capacities, the Employee shall perform such
services and duties in connection with the business, affairs and operations of
the Company as may be assigned or delegated to the Employee from time to time by
or under the authority of the Board of Directors. The Employee shall be
principally located at the Company's Boston office.

         (b) Employee agrees to his employment as described in this Paragraph 2
and agrees to devote substantially ALL of his working time and efforts to the
performance of his duties hereunder, except as otherwise approved by the Board
of Directors. Notwithstanding the foregoing, nothing herein shall be interpreted
to preclude Employee from (i) engaging in

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Minority Interest Passive Investments (as defined below), including Minority
Interest Passive Investments in, or relating to the ownership, development,
operation, management, or leasing of, commercial real estate properties or (ii)
participating as an officer or director of, or advisor to, any charitable or
other tax exempt organization; PROVIDED that such activities and related duties
and pursuits do not restrict Employee's ability to fulfill his obligations as an
officer and employee of the Company as set forth herein.

     Engaging in a "MINORITY INTEREST PASSIVE INVESTMENT" means acquiring,
holding, and exercising the voting rights associated with an investment made
through (i) the purchase of securities (including partnership interests) that
represent a non-controlling, minority interest in an entity or (ii) the lending
of money, in either case with the purpose or intent of obtaining a return on
such investment but without management by Employee of the property or business
to which such investment directly or indirectly relates and without any business
or strategic consultation by Employee with such entity.

     3.  COMPENSATION.

         (a) BASE SALARY. The Company shall pay Employee an annual salary of Two
Hundred Sixty-Five Thousand Dollars ($265,000) (the "BASE SALARY"), payable in
accordance with the Company's normal business practices for senior executives
(including tax withholding), but in no event less frequently than monthly.
Employee's Base Salary shall be reviewed at least annually by the Board of
Directors or the Compensation Committee of the Board of Directors (the
"COMPENSATION COMMITTEE") and may be increased but not decreased in its
discretion.

         (b) BONUS. On each annual compensation determination date established
by the Company during the Term, the Company shall review the performance of the
Company and of Employee during the prior year, and the Company may provide
Employee with additional compensation as a bonus if the Board of Directors, or
the Compensation Committee, in its discretion, determines that Employee's
contribution to the Company warrants such additional payment and the Company's
anticipated financial performance for the present period permits such payment.

     4.  BENEFITS.

         (a) MEDICAL/DENTAL INSURANCE. Employee shall be entitled to participate
in any and all employee benefit plans, including all medical and dental
insurance plans as in effect from time to time for senior executives of the
Company. Such participation shall be subject to (i) the terms of the applicable
plan documents, (ii) generally applicable policies of the Company, and (iii) the
discretion of the Board of Directors, the Compensation Committee or any
administrative or other committee provided for in, or contemplated by, such
plan. Nothing contained in this Agreement shall be construed to create any
obligation on the part of the Company to establish any such plan or to maintain
the effectiveness of any such plan which may be in effect from time to time.

         (b) LIFE INSURANCE/DISABILITY INSURANCE. The Company shall provide
Employee with such life and/or disability insurance as the Company may from time
to time make available to senior executives of the Company.

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         (c) EXPENSES. The Company shall promptly reimburse Employee for all
reasonable business expenses incurred by Employee in accordance with the
practices of the Company for senior executives of the Company, as in effect from
time to time.

         (d) VACATION. Employee shall receive paid vacation annually in
accordance with terms determined for such Employee by the Company, but in no
event shall Employee receive less than four weeks of paid vacation per year.

         (e) STOCK OPTIONS; RESTRICTED STOCK. Employee shall be entitled to
grants of stock options and restricted stock awards in an amount to be
determined by the Compensation Committee in its discretion under the Boston
Properties, Inc. 1997 Stock Option and Incentive Plan or any other stock option
plan adopted by the Company from time to time (the "STOCK OPTION PLAN").

         (f) DEFERRED COMPENSATION. Employee shall be entitled to participate in
any deferred compensation plan or arrangement that the Company may have in place
for its senior executives and/or officers.

         (g) AUTOMOBILE. The Company shall provide Employee with an automobile
allowance of Seven Hundred Fifty Dollars ($750) per month, such amount to be
increased from time to time in the Company's sole discretion and to be paid to
Employee no less frequently than monthly.

         (h) OTHER BENEFITS. The Company shall provide to Employee such other
benefits, including the right to participate in such retirement or pension
plans, as are made generally available to senior executives of the Company from
time to time. Such participation shall be subject to (i) the terms of the
applicable plan documents, (ii) generally applicable policies of the Company,
and (iii) the discretion of the Board of Directors, the Compensation Committee,
or any administrative or other committee provided for in, or contemplated by,
such plan.

         (i) TAXATION OF PAYMENTS AND BENEFITS. The Company shall undertake to
make deductions, withholdings and tax reports with respect to payments and
benefits under this Agreement to the extent that it reasonably and in good faith
believes that it is required to make such deductions, withholdings and tax
reports. Payments under this Agreement shall be in amounts net of any such
deductions or withholdings. Nothing in this Agreement shall be construed to
require the Company to make any payments to compensate the Employee for any
adverse tax effect associated with any payments or benefits or for any deduction
or withholding from any payment or benefit.

     5.  INDEMNIFICATION. To the full extent permitted by law and subject to the
Company's Certificate of Incorporation and Bylaws, the Company shall indemnify
Employee with respect to any actions commenced against Employee in his capacity
as a director or officer or former director or officer of the Company, or any
affiliate thereof for which he may serve in such capacity, and the Company shall
advance on a timely basis any expenses incurred in defending such actions. The
obligation to indemnify hereunder shall survive the termination of

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this Agreement. The Company agrees to use its best efforts to secure and
maintain directors' and officers' liability insurance with respect to Employee.

     6.  COMPANY AUTHORITY/POLICIES. Employee agrees to observe and comply with
the rules and regulations of the Company as adopted by its Board of Directors
respecting the performance of his duties and to carry out and perform orders,
directions and policies communicated to him from time to time by the Board of
Directors.

     7.  RECORDS/NONDISCLOSURE/COMPANY POLICIES.

         (a) GENERAL. All records, financial statements and similar documents
obtained, reviewed or compiled by Employee in the course of the performance by
him of services for the Company, whether or not confidential information or
trade secrets, shall be the exclusive property of the Company. Employee shall
have no rights in such documents upon any termination of this Agreement.

         (b) CONFIDENTIAL INFORMATION. Employee will not disclose to any person
or entity (except as required by applicable law, the rules of the New York Stock
Exchange, or otherwise in connection with the performance of his duties and
responsibilities hereunder), or use for his own benefit or gain, any
confidential information of the Company obtained by him incident to his
employment with the Company. Employee shall take all reasonable steps to
safeguard any confidential information and to protect such confidential
information against disclosure, misuse, loss, or theft. The term "CONFIDENTIAL
INFORMATION" includes, without limitation, financial information, business
plans, prospects, and opportunities which have been discussed or considered by
the management of the Company, but does not include any information which has
become part of the public domain by means other than Employee's non-observance
of his obligations hereunder.

     This Paragraph 7 shall survive the termination of this Agreement.

     8.  TERMINATION/SEVERANCE.

         (a) GENERAL.

             (i)    AT WILL EMPLOYMENT. Employee's employment hereunder is "at
will" and, therefore, may be terminated at any time, with or without cause, at
the option of the Company, subject only to the severance obligations under this
Paragraph 8.

             (ii)   NOTICE OF TERMINATION. Except for termination as a result of
Employee's death as specified in Subparagraph 8(b), any termination of
Employee's employment by the Company or any such termination by Employee shall
be communicated by written Notice of Termination to the other party hereto. For
purposes of this Agreement, a "NOTICE OF TERMINATION" shall mean a notice which
shall indicate the specific termination provision hereunder relied upon by the
terminating party.

             (iii)  DATE OF TERMINATION. "DATE OF TERMINATION" shall mean: (A)
if Employee's employment is terminated by his death, the date of his death; (B)
if Employee's employment is terminated on account of disability under
Subparagraph 8(c), the date on which

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Notice of Termination is given; (C) if Employee's employment is terminated by
the Company for Cause under Subparagraph 8(d), the date on which a Notice of
Termination is given; (D) if Employee's employment is terminated by the Company
without Cause under Subparagraph 8(e)(i), thirty (30) days after the date on
which a Notice of Termination is given; and (E) if Employee's employment is
terminated by Employee under Subparagraph 8(e)(ii) or 8(f), thirty (30) days
after the date on which a Notice of Termination is given.

         (b) DEATH. Employee's employment hereunder shall terminate upon his
death. If Employee's employment terminates by reason of his death, the Company
shall, within ninety (90) days of death, pay in a lump sum amount to such person
as Employee shall designate in a notice filed with the Company or, if no such
person is designated, to Employee's estate, Employee's accrued and unpaid Base
Salary to his date of death, plus his accrued and unpaid target bonus, prorated
for the number of days actually employed in the then current calendar year. All
unvested stock options and stock-based grants shall immediately vest in
Employee's estate or other legal representatives and become exercisable or
nonforfeitable, and Employee's estate or other legal representatives shall have
such period of time to exercise the stock options as is provided in the Stock
Option Plan and agreements with Employee pursuant thereto. For a period of
eighteen (18) months following the Date of Termination, and subject to the
continued copayment of premium amounts by the Employee's spouse and dependents,
the Employee's spouse and dependents shall continue to participate in the
Company's health insurance plan upon the same terms and conditions in effect on
the Date of Termination, PROVIDED, HOWEVER, that the continuation of health
benefits under this Subparagraph shall reduce and count against the rights of
the Employee's spouse and dependents under the Consolidated Omnibus Budget
Reconciliation Act of 1985, as amended ("COBRA"). In addition to the foregoing,
any payments to which Employee's spouse, beneficiaries, or estate may be
entitled under any employee benefit plan shall also be paid in accordance with
the terms of such plan or arrangement. Such payments, in the aggregate, shall
fully discharge the Company's obligations hereunder.

         (c) DISABILITY. If, as a result of Employee's incapacity due to
physical or mental illness, Employee shall have been absent from his duties
hereunder on a full-time basis for one hundred eighty (180) calendar days in the
aggregate in any twelve (12) month period, the Company may terminate Employee's
employment hereunder. During any period that Employee fails to perform his
duties hereunder as a result of incapacity due to physical or mental illness,
Employee shall continue to receive his accrued and unpaid Base Salary and
accrued and unpaid target bonus, prorated for the number of days actually
employed in the then current calendar year, until Employee's employment is
terminated due to disability in accordance with this Subparagraph (c) or until
Employee terminates his employment in accordance with Subparagraph (e)(ii) or
(f), if earlier. All unvested stock options and stock-based grants shall
immediately vest and become exercisable or nonforfeitable, and Employee shall
have such period of time to exercise the stock options as is provided in the
Stock Option Plan and agreements with Employee pursuant thereto. For a period of
eighteen (18) months following the Date of Termination and subject to the
Employee's continued copayment of premium amounts, the Employee, Employee's
spouse and dependents shall continue to participate in the Company's health
insurance plan upon the same terms and conditions in effect on the Date of
Termination, PROVIDED, HOWEVER, that the continuation of health benefits under
this Subparagraph shall reduce and count against Employee's rights under COBRA.
In addition to the foregoing, any payments

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to which Employee may be entitled under any employee benefit plan shall also be
paid in accordance with the terms of such plan or arrangement. Such payments, in
the aggregate, shall fully discharge the Company's obligations hereunder.

         (d) TERMINATION BY THE COMPANY FOR CAUSE.

             (i)    The Company may terminate Employee's employment hereunder
for Cause. "CAUSE" shall mean: (A) gross negligence or willful misconduct by
Employee in connection with the performance of his material duties hereunder;
(B) a breach by Employee of any of his material duties hereunder (for reasons
other than physical or mental illness) and the failure of Employee to cure such
breach within thirty (30) days after written notice thereof by the Company; (C)
conduct by Employee against the material best interests of the Company or a
material act of common law fraud against the Company or its affiliates or
employees; or (D) indictment of Employee of a felony and such indictment has a
material adverse affect on the interests or reputation of the Company.

             (ii)   If Employee's employment is terminated by the Company for
Cause, then the Company shall, through the Date of Termination, pay Employee his
accrued and unpaid Base Salary. Thereafter, the Company shall have no further
obligations to Employee except as otherwise provided hereunder; PROVIDED that
any such termination shall not adversely affect or alter Employee's rights under
any employee benefit plan of the Company in which Employee, at the Date of
Termination, has a vested interest, unless otherwise provided in such employee
benefit plan or any agreement or other instrument attendant thereto.
Notwithstanding the foregoing and in addition to whatever other rights or
remedies the Company may have at law or in equity, all stock options and other
stock-based grants held by Employee, whether vested or unvested as of the Date
of Termination, shall immediately expire on the Date of Termination if
Employee's employment is terminated by the Company for Cause.

         (e) TERMINATION BY THE COMPANY WITHOUT CAUSE OR BY EMPLOYEE FOR GOOD
REASON.

             (i)    The Company may terminate Employee's employment hereunder
without Cause if such termination is approved by the Chief Executive Officer or
Chairman of the Company. Any termination by the Company of Employee's employment
hereunder which does not (A) constitute a termination for Cause under
Subparagraph (d)(i), (B) result from the death or disability of the Employee
under Subparagraph (b) or (c), or (C) result from the expiration of the Term,
shall be deemed a termination without Cause.

             (ii)   Employee may terminate his employment hereunder for Good
Reason. "GOOD REASON" shall mean: (A) a substantial adverse change, not
consented to by Employee, in the nature or scope of Employee's responsibilities,
authorities, powers, functions, or duties under this Agreement; (B) a breach by
the Company of any of its material obligations hereunder and the failure of the
Company to cure such breach within thirty (30) days after written notice thereof
by Employee; or (C) the involuntary relocation of the Company's offices at which
Employee is principally employed to a location more than fifty (50) miles from
such offices, or the requirement by the Company that Employee be based anywhere
other than the Company's offices at such location on an extended basis, except
for required travel on the

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Company's business to an extent substantially consistent with Employee's
business travel obligations.

             (iii)  If Employee's employment is terminated by the Company
without Cause or if Employee terminates his employment for Good Reason in
accordance with this Subparagraph (e), then the Company shall, through the Date
of Termination, pay Employee his accrued and unpaid Base Salary and his accrued
and unpaid target bonus prorated for the number of days actually employed in the
then current calendar year. In addition, subject to signing by Employee of a
general release of claims in a form and manner satisfactory to the Company, the
Employee shall be entitled to the following:

                    (A) Salary continuation in an amount (the "SEVERANCE
AMOUNT") equal to the sum of (x) his annual Base Salary under Subparagraph 3(a)
and (y) the amount of his cash bonus, if any, received in respect of the
immediately preceding year under Subparagraph 3(b). The Severance Amount shall
be paid in equal monthly installments over a twelve (12) month period;

                    (B) All stock options and other stock-based awards, granted
to Employee after the Effective Date, in which Employee would have vested if he
had remained employed for a period of twelve (12) months commencing on the Date
of Termination, shall vest and become exercisable or nonforfeitable as of the
Date of Termination;

                    (C) Subject to the Employee's continued copayment of premium
amounts, continued participation for twelve (12) months in the Company's health
insurance plan upon the same terms and conditions in effect on the Date of
Termination, PROVIDED, HOWEVER, that the continuation of health benefits under
this Subparagraph shall reduce and count against Employee's rights under COBRA;
and

                    (D) Subject to (B) above, all rights and benefits granted or
in effect with respect to Employee under the Stock Option Plan and agreements
with Employee pursuant thereto.

         (f) VOLUNTARY TERMINATION BY EMPLOYEE. Employee may terminate his
employment hereunder for any reason, including, but not limited to, Good Reason
in accordance with Subparagraph (e)(ii). If Employee's employment is terminated
by Employee other than for Good Reason, then the Company shall, through the Date
of Termination, pay Employee his accrued and unpaid Base Salary. Thereafter, the
Company shall have no further obligations to Employee except as otherwise
expressly provided hereunder; PROVIDED any such termination shall not adversely
affect or alter Employee's rights under any employee benefit plan of the Company
in which Employee, at the Date of Termination, has a vested interest, unless
otherwise provided in such employee benefit plan or any agreement or other
instrument attendant thereto. The vesting and exercise of any stock options and
the forfeitability of any stock-based grants held by Employee shall be governed
by the terms of the Stock Option Plan and the related agreements between
Employee and the Company

         (g) NO MITIGATION. Without regard to the reason for the termination of
Employee's employment hereunder, Employee shall be under no obligation to
mitigate damages

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with respect to such termination under any circumstances and in the event
Employee is employed or receives income from any other source, there shall be no
offset against the amounts due from the Company hereunder.

     9.  NONCOMPETITION. Because Employee's services to the Company are special
and because Employee has access to the Company's confidential information,
Employee covenants and agrees that during the Employment Period and until the
end of a one-year period following the termination of Employee's employment with
the Company for any reason, Employee shall not, without the prior written
consent of the Company (which shall be authorized by approval of the Board of
Directors of the Company, including the approval of a majority of the
independent Directors of the Company), directly or indirectly:

         (a) engage, participate or assist in, either individually or as an
owner, partner, employee, consultant, director, officer, trustee, or agent of
any business that engages or attempts to engage in, directly or indirectly, the
acquisition, development, construction, operation, management, or leasing of any
commercial real estate property in any of the Company's Markets (as hereinafter
defined) at the time of Employee's termination of employment;

         (b) intentionally interfere with, disrupt or attempt to disrupt the
relationship, contractual or otherwise, between the Company or its affiliates
and any tenant, supplier, contractor, lender, employee, or governmental agency
or authority; or

         (c) call upon, compete for, solicit, divert, or take away, or attempt
to divert or take away any of the tenants or employees of the Company or its
affiliates, either for himself or for any other business, operation,
corporation, partnership, association, agency, or other person or entity.

     "MARKET" as used herein means an area covering a 25 mile radius around (x)
any property or land owned by the Company, under development by the Company or
with respect to which the Company has an agreement or option to acquire a
property, development or land or (y) any property or development for which the
Company provides third party development or management services; PROVIDED that
for any such property, development or land located in New York City, no such
radial area shall extend beyond New York City.

     This Paragraph 9 shall not be interpreted to prevent Employee from engaging
in Minority Interest Passive Investments or any other activity permitted under
Subparagraph 2(b). This Paragraph 9 shall survive the termination of this
Agreement.

     Notwithstanding anything to the contrary herein, the noncompetition
provision of this Paragraph 9 shall not apply if Employee's employment
terminates after a Change in Control (as defined in the Severance Plan).

     10. CHANGE IN CONTROL PAYMENTS. Notwithstanding anything to the contrary in
the foregoing, in the event that the Employee's employment terminates after a
Change in Control (as defined in the Severance Plan) under circumstances that
would entitle him to payments and benefits under the Severance Plan, he shall
not be entitled to receive any payments or benefits under this Agreement.

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     11. CONFLICTING AGREEMENTS. Employee hereby represents and warrants that
the execution of this Agreement and the performance of his obligations hereunder
will not breach or be in conflict with any other agreement to which he is a
party or is bound, and that he is not now subject to any covenants against
competition or similar covenants which would affect the performance of his
obligations hereunder.

     12. NOTICES. All notices, requests, demands, and other communications under
this Agreement shall be in writing and shall be deemed duly given (i) if
delivered by hand and receipted for by the party addressee, on the date of such
receipt or (ii) if mailed by domestic certified or registered mail with postage
prepaid, on the third business day after the date postmarked. Address for notice
for the Company is as shown above, or as subsequently modified by written
notice. Address for notice for the Employee is the address shown on the records
of the Company.

     13. INTEGRATION. This Agreement constitutes the entire agreement between
the parties with respect to the subject matter hereof and supersedes all prior
agreements between the parties with respect to any related subject matter,
provided, however, that the Severance Plan, as amended from time to time, shall
remain in full force and effect hereafter.

     14. ASSIGNMENT; SUCCESSORS AND ASSIGNS, ETC. Neither the Company nor the
Employee may make any assignment of this Agreement or any interest herein, by
operation of law or otherwise, without the prior written consent of the other
party; provided that the Company may assign its rights under this Agreement
without the consent of the Employee in the event that the Company shall effect a
reorganization, consolidate with or merge into any other corporation,
partnership, organization or other entity, or transfer all or substantially all
of its properties or assets to any other corporation, partnership, organization
or other entity. This Agreement shall inure to the benefit of and be binding
upon the Company and the Employee, their respective successors, executors,
administrators, heirs and permitted assigns.

     15. MISCELLANEOUS. Headings herein are for convenience of reference only
and shall not define, limit or interpret the contents hereof.

     16. AMENDMENT. This Agreement may be amended, modified or supplemented by
the mutual consent of the parties in writing, but no oral amendment,
modification or supplement shall be effective.

     17. ARBITRATION; OTHER DISPUTES. Any dispute or controversy arising under
or in connection with this Agreement shall be settled exclusively by arbitration
in Boston, Massachusetts, in accordance with the rules of the American
Arbitration Association then in effect. Judgment may be entered in any court
having jurisdiction. Notwithstanding the above, the Company shall be entitled to
seek a restraining order or injunction in any court of competent jurisdiction to
prevent any continuation of any violation of Paragraph 7 or 9 hereof. In the
event that the Company terminates Employee's employment for Cause under
Subparagraph 8(d)(i) and Employee contends that Cause did not exist, then the
Company's only obligation shall be to submit such claim to arbitration and the
only issue before the arbitrator will be whether Employee was in fact terminated
for Cause. If the arbitrator determines that Employee was not terminated for
Cause by the Company, then the only remedies that the arbitrator may award are

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(i) the Severance Amount specified in Subparagraph 8(e)(iii)(A), (ii) the costs
of arbitration, (iii) Employee's reasonable attorneys' fees, (iv) the additional
vesting of Employee's stock options and other stock-based awards in accordance
with Subparagraph 8(e)(iii)(B), and (v) the continued participation in the
Company's health insurance plan in accordance with Subparagraph 8(e)(iii)(C). If
the arbitrator finds that Employee was terminated for Cause, the arbitrator will
be without authority to award Employee anything, and the parties will each be
responsible for their own attorneys' fees, and they will divide the costs of
arbitration equally. Furthermore, should a dispute occur concerning Employee's
mental or physical capacity as described in Subparagraph 8(c), a doctor selected
by Employee and a doctor selected by the Company shall be entitled to examine
Employee. If the opinion of the Company's doctor and Employee's doctor conflict,
the Company's doctor and Employee's doctor shall together agree upon a third
doctor, whose opinion shall be binding. This Paragraph 17 shall survive the
termination of this Agreement.

     18. LITIGATION AND REGULATORY COOPERATION. During and after Employee's
employment, Employee shall reasonably cooperate with the Company in the defense
or prosecution of any claims or actions now in existence or which may be brought
in the future against or on behalf of the Company which relate to events or
occurrences that transpired while Employee was employed by the Company; provided
that such cooperation shall not materially and adversely affect Employee or
expose Employee to an increased probability of civil or criminal litigation.
Employee's cooperation in connection with such claims or actions shall include,
without limitation, being available to meet with counsel to prepare for
discovery or trial and to act as a witness on behalf of the Company at mutually
convenient times. During and after Employee's employment, Employee also shall
cooperate fully with the Company in connection with any investigation or review
of any federal, state or local regulatory authority as any such investigation or
review relates to events or occurrences that transpired while Employee was
employed by the Company. The Company shall also provide Employee with
compensation on an hourly basis calculated at his final base compensation rate
for requested litigation and regulatory cooperation that occurs after his
termination of employment, and reimburse Employee for all costs and expenses
incurred in connection with his performance under this Paragraph 18, including,
without limitation, reasonable attorneys' fees and costs.

     19. SEVERABILITY. If any provision of this Agreement shall to any extent be
held void or unenforceable (as to duration, scope, activity, subject or
otherwise) by a court of competent jurisdiction, such provision shall be deemed
to be modified so as to constitute a provision conforming as nearly as possible
to the original provision while still remaining valid and enforceable. In such
event, the remainder of this Agreement (or the application of such provision to
persons or circumstances other than those in respect of which it is deemed to be
void or unenforceable) shall not be affected thereby. Each other provision of
this Agreement, unless specifically conditioned on the voided aspect of such
provision, shall remain valid and enforceable to the fullest extent permitted by
law; any other provisions of this Agreement that are specifically conditioned on
the voided aspect of such invalid provision shall also be deemed to be modified
so as to constitute a provision conforming as nearly as possible to the original
provision while still remaining valid and enforceable to the fullest extent
permitted by law.

     20. GOVERNING LAW. This Agreement shall be construed and regulated in all
respects under the laws of the State of Delaware.

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     21. COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which when so executed and delivered shall be taken to be
an original; but such counterparts shall together constitute one and the same
document.

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     IN WITNESS WHEREOF, this Agreement is entered into as of the date and year
first above written.

                                             BOSTON PROPERTIES, INC.

                                             By: /s/ Edward H. Linde
                                                 -------------------------------
                                                 Name:  Edward H. Linde
                                                 Title: President and
                                                        Chief Executive Officer


                                             /s/ Bryan J. Koop
                                             -----------------------------------
                                             Bryan J. Koop

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