UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DCD.C. 20549

FORM 10-K

For the fiscal year ended December 31, 20102012

OR

For the transition period from                      to                     

Commission file numberFile Number: 1-13087

BOSTON PROPERTIES, INC.

(Exact name of registrantRegistrant as specified in its charter)

Registrant’s telephone number, including area code: (617) 236-3300

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  x    No  ¨

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.    Yes  ¨    No  x

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer  x             Accelerated filer  ¨            Non-accelerated filer  ¨                Smaller reporting company  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act).    Yes  ¨    No  x

As of June 30, 2010,29, 2012, the aggregate market value of the 136,327,099149,019,383 shares of common stock held by non-affiliates of the Registrant was $9,725,575,243$16,149,230,581 based upon the last reported sale price of $71.34$108.37 per share on the New York Stock Exchange on June 30, 2010.29, 2012. (For this computation, the Registrant has excluded the market value of all shares of Common Stock reported as beneficially owned by executive officers and directors of the Registrant; such exclusion shall not be deemed to constitute an admission that any such person is an affiliate of the Registrant.)

As of February 18, 2011,21, 2013, there were 141,864,497151,639,342 shares of Common Stock outstanding.

Certain information contained in the Registrant’s Proxy Statement relating to its Annual Meeting of Stockholders to be held May 17, 201121, 2013 is incorporated by reference in Items 10, 11, 12, 13 and 14 of Part III. The Registrant intends to file such Proxy Statement with the Securities and Exchange Commission not later than 120 days after the end of its fiscal year ended December 31, 2010.

2012.

TABLE OF CONTENTS

PART I

General

As used herein, the terms “we,” “us,” “our” and the “Company” refer to Boston Properties, Inc., a Delaware corporation organized in 1997, individually or together with its subsidiaries, including Boston Properties Limited Partnership, a Delaware limited partnership, and our predecessors. We are a fully integrated, self-administered and self-managed real estate investment trust, or “REIT,” and one of the largest owners and developers of office properties in the United States.

Our properties are concentrated in five markets—Boston, Washington, DC, midtown Manhattan,New York, Princeton, San Francisco and Princeton, NJ.Washington, DC. We conduct substantially all of our business through our subsidiary, Boston Properties Limited Partnership. At December 31, 2010,2012, we owned or had interests in 146157 properties, totaling approximately 39.944.4 million net rentable square feet, including fivenine properties under construction totaling approximately 2.02.8 million net rentable square feet. In addition, we had structured parking for approximately 40,66446,833 vehicles containing approximately 13.715.9 million square feet. Our properties consisted of:

We own or control undeveloped land totaling approximately 513.3509.3 acres, which could support approximately 12.812.5 million square feet of additional development. In addition, we have a noncontrolling interest in the Boston Properties Office Value-Added Fund, L.P., which we refer to as the “Value-Added Fund,” which is a strategic partnership with two institutional investors through which we have pursued the acquisition of assets within our existing markets that havehad deficiencies in property characteristics that provideprovided an opportunity to create value through repositioning, refurbishment or renovation. Our investments through the Value-Added Fund are not included in our portfolio information tables or any other portfolio level statistics. At December 31, 2010,2012, the Value-Added Fund had investments in an23 buildings comprised of two office property in Chelmsford, Massachusetts and complexes in Mountain View, California.

We consider Class A office properties to be centrally-located buildings that are professionally managed and maintained, attract high-quality tenants and command upper-tier rental rates, and that are modern structures or have been modernized to compete with newer buildings. We consider Office/Technical properties to be properties that support office, research and development, laboratory and other technical uses. Our definitions of Class A office and Office/Technical properties may be different than those used by other companies.

We are a full-service real estate company, with substantial in-house expertise and resources in acquisitions, development, financing, capital markets, construction management, property management, marketing, leasing, accounting, tax and legal services. As of December 31, 2010,2012, we had approximately 680730 employees. Our thirty-fourthirty-three senior officers have an average of twenty-sixtwenty-eight years experience in the real estate industry, including an average of sixteeneighteen years of experience with us. Our principal executive office and Boston regional office isare located at The Prudential Center, 800 Boylston Street, Suite 1900, Boston, Massachusetts 02199 and our telephone number is (617) 236-3300. In addition, we have regional offices at 505 9^th Street, NW, Washington, DC 20004; 599 Lexington Avenue, New York, New York 10022; 302 Carnegie Center, Princeton, New Jersey 08540; Four Embarcadero Center, San Francisco, California 94111; and 302 Carnegie Center, Princeton, New Jersey 08540.2200 Pennsylvania Avenue NW, Washington, DC 20037.

Our Web site is located at http://www.bostonproperties.com. On our Web site, you can obtain a free copy of our annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and amendments

to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, as soon as reasonably practicable after we electronically file such material with, or furnish it to, the Securities and Exchange Commission, or the SEC. You may also obtain our reports by accessing the EDGAR database at the SEC’s website at http://www.sec.gov, or we will furnish an electronic or paper copy of these reports free of charge upon written request to: Investor Relations, Boston Properties, Inc., The Prudential Center, 800 Boylston Street, Suite 1900, Boston, Massachusetts 02199. The name “Boston Properties” and our logo (consisting of a stylized “b”) are registered service marks of Boston Properties Limited Partnership.

Boston Properties Limited Partnership

Boston Properties Limited Partnership, or BPLP or our Operating Partnership, is a Delaware limited partnership, and the entity through which we conduct substantially all of our business and own, either directly or through subsidiaries, substantially all of our assets. We are the sole general partner and, as of February 18, 2011,21, 2013, the owner of approximately 86.3%89.0% of the economic interests in BPLP. Economic interest was calculated as the number of common partnership units of BPLP owned by the Company as a percentage of the sum of (1) the actual aggregate number of outstanding common partnership units of BPLP, (2) the number of common partnership units issuable upon conversion of outstanding preferred partnership units of BPLP and (3) the number of common units issuable upon conversion of all outstanding long term incentive plan units of BPLP, or LTIP Units, other than LTIP Units issued in the form of 2011 Outperformance Awards (“2011 OPP Awards”) and 2013 Multi-Year Long-Term Incentive Plan Awards (“MYLTIP Awards”), assuming all conditions have been met for the conversion of the LTIP Units. Refer to Note 20 to the Consolidated Financial Statements. An LTIP Unit is generally the economic equivalent of a share of our restricted common stock, although LTIP Units issued in the form of 2011 OPP Awards or MYLTIP Awards are only entitled to receive one-tenth (1/10^th) of the regular quarterly distributions (and no special distributions) prior to being earned. Our general and limited partnership interests in BPLP entitle us to share in cash distributions from, and in the profits and losses of, BPLP in proportion to our percentage interest and entitle us to vote on all matters requiring a vote of the limited partners. The other limited partners of BPLP are persons who contributed their direct or indirect interests in properties to BPLP in exchange for common units or preferred units of limited partnership interest in BPLP or recipients of LTIP Units pursuant to the Second Amendment and Restatement of our 1997 Stock Option and Incentive Plan (the “1997 Plan”).Plan. Under the limited partnership agreement of BPLP, unitholders may present their common units of BPLP for redemption at any time (subject to restrictions agreed upon at the time of issuance of the units that may restrict such right for a period of time, generally one year from issuance). Upon presentation of a unit for redemption, BPLP must redeem the unit for cash equal to the then value of a share of our common stock. In lieu of cash redemption by BPLP, however, we may elect to acquire any common units so tendered by issuing shares of our common stock in exchange for the common units. If we so elect, our common stock will be exchanged for common units on a one-for-one basis. This one-for-one exchange ratio is subject to specified adjustments to prevent dilution. We generally expect that we will elect to issue our common stock in connection with each such presentation for redemption rather than having BPLP pay cash. With each such exchange or redemption, our percentage ownership in BPLP will increase. In addition, whenever we issue shares of our common stock other than to acquire common units of BPLP, we must contribute any net proceeds we receive to BPLP and BPLP must issue to us an equivalent number of common units of BPLP. This structure is commonly referred to as an umbrella partnership REIT, or “UPREIT.”UPREIT.

Preferred units of BPLP have the rights, preferences and other privileges including the right to convert into common units of BPLP, as are set forth in an amendment to the limited partnership agreement of BPLP. As of December 31, 20102012 and February 18, 2011,21, 2013, BPLP had onetwo series of its preferred units outstanding.Preferred Units outstanding (i.e., Series Two Preferred Units and Series Four Preferred Units). The Series Two Preferred Units have a liquidation preference of $50.00 per unit (or an aggregate of approximately $55.7$49.8 million at December 31, 20102012 and February 18, 2011)21, 2013). The Series Two Preferred Units are convertible, at the holder’s election, into common units at a conversion price of $38.10 per common unit (equivalent to a ratio of 1.312336 common units per Series Two Preferred Unit). Distributions on the Series Two Preferred Units are payable quarterly and, unless the greater rate described in the next sentence applies, accrue at 6.0% per annum. If

distributions on the number of common units of limited partnership interest, or OP Units, into which the Series Two Preferred Units are convertible are greater than distributions calculated using the rate described in the preceding sentence for the applicable quarterly period, then the greater distributions are payable instead. The holders of Series Two Preferred Units have the right to require BPLP to redeem their units for cash at the redemption price of $50.00 per unit on May 12, 2011, May 14, 2012, May 14, 2013 and May 12, 2014. The maximum number of units that may be required to be redeemed from all holders on each of these dates is 1,007,662, which is one-sixth of the number of Series Two

Preferred Units that were originally issued. The holders also had the right to have their Series Two Preferred Units redeemed for cash as of May 12, 2009, and May 12, 2010, May 12, 2011 and May 14, 2012, although no holder exercised such right. On May 14, 2013 and May 12, 2014, BPLP also has the right, undersubject to certain conditions, and at certain times, to redeem Series Two Preferred Units for cash andor to convert into OP Units any Series Two Preferred Units that are not redeemed when they are eligible for redemption.

The Series Four Preferred Units have a liquidation preference of $50.00 per unit (or an aggregate of approximately $61.1 million at December 31, 2012 and February 21, 2013). The Series Four Preferred Units, which bear a preferred distribution equal to 2.00% per annum on a liquidation preference of $50.00 per unit, are not convertible into or exchangeable for any common equity of BPLP or us. We also have the right, subject to certain conditions, to redeem Series Four Preferred Units for cash at the redemption price of $50.00 per unit. Due to the holders’ redemption option existing outside the control of the Company, the Series Four Preferred Units are presented outside of permanent equity in our Consolidated Balance Sheets.

Transactions During 20102012

Acquisitions

On JulyMarch 1, 2010,2012, we acquired the mortgage loan collateralized by a land parcel zoned for residential use453 Ravendale Drive located in Reston, Virginia for approximately $20.3 million. In connection with the acquisition of the loan, we entered into a forbearance agreement pursuant to which we obtained the fee interest in the land by deed in lieu of foreclosure.

On September 24, 2010, we acquired fee title to 510 Madison Avenue in New York CityMountain View, California for a purchase price of approximately $287.0 million.$6.7 million in cash. 453 Ravendale Drive is an approximately 30,000 net rentable square foot Office/Technical property.

On March 13, 2012, we acquired 100 Federal Street in Boston, Massachusetts for an aggregate investment of approximately $615.0 million in cash. In connection with the acquisition,transaction, we also incurredentered into a long-term lease with an affiliate of Bank of America for approximately $1.5 million of acquisition costs that were expensed during the year ended December 31, 2010. Previously, on August 10, 2010, we had acquired the junior mezzanine loan that was secured by a pledge of a subordinate ownership interest in the property for a purchase price of approximately $22.5 million. 510 Madison Avenue732,000 square feet. 100 Federal Street is an approximately 347,0001,265,000 net rentable square foot, 37-story Class A office tower which is currently under development. In connection with the acquisition, we assumed the mortgage loan totaling approximately $202.6 million and, at closing, we caused the assignment of the mortgage to a new lender and subsequently increased the amount borrowed to $267.5 million. This amount is fully secured by cash deposits included within “Cash Heldlocated in Escrows” in our Consolidated Balance Sheets. The mortgage financing bears interest at a variable rate equal to LIBOR plus 0.30% per annum and matures on February 24, 2012.Boston, Massachusetts.

On September 27, 2010, we entered into an agreement to acquire Bay Colony Corporate Center in Waltham, Massachusetts. On February 1, 2011,October 4, 2012, we completed the acquisition forformation of a joint venture which owns and operates Fountain Square located in Reston, Virginia, adjacent to our other Reston properties. Fountain Square is an aggregate purchase priceoffice and retail complex aggregating approximately 758,000 net rentable square feet, comprised of approximately $185.0 million.521,000 net rentable square feet of Class A office space and approximately 237,000 net rentable square feet of retail space. The purchase price consisted ofjoint venture partner contributed the property valued at approximately $41.1$385.0 million ofand related mortgage indebtedness totaling approximately $211.3 million for a 50% interest in the joint venture. We contributed cash andtotaling approximately $87.0 million for our 50% interest, which cash was distributed to the assumption of approximately $143.9 million of indebtedness.joint venture partner. We are consolidating this joint venture. The assumed debt is a securitized senior mortgage loan that bears interest at a fixed rate of 6.53%5.71% per annum and matures on JuneOctober 11, 2012. The loan requires interest-only payments with a balloon payment due at maturity. Bay Colony Corporate Center is an approximately 1,000,000 net rentable square foot, four-building Class A office park situated2016. Pursuant to the joint venture agreement (i) we have rights to acquire the partner’s 50% interest and (ii) the partner has the right to cause us to acquire the partner’s interest on a 58-acre siteJanuary 4, 2016, in Waltham, Massachusetts.

On December 29, 2010, we completed the acquisition of the John Hancock Tower and Garage in Boston, Massachusetts for an aggregate purchase price of approximately $930.0 million. The purchase price consisted of approximately $289.5 million of cash and the assumption of approximately $640.5 million of indebtedness. The assumed debt is a securitized senior mortgage loan that bears interesteach case at a fixed rate of 5.68% per annum and maturesprice totaling approximately $102.0 million in cash. The fixed price option rights expire on January 6, 2017. The loan requires interest-only payments with a balloon payment due at maturity. In connection with the acquisition, we incurred an aggregate of approximately $0.9 million of acquisition costs that were expensed during the year ended December 31, 2010. The John Hancock Tower is an iconic 62-story, approximately 1,700,000 rentable square foot office tower located in the heart of Boston’s Back Bay neighborhood. The garage is an eight-level, 2,013 space parking facility. The seller has agreed to (1) fund the cost of and complete certain capital projects and (2) fund the cost of certain tenant improvements, both of which are currently underway, totaling approximately $46.0 million. Refer to Note 3 to the Consolidated Financial Statements.

Dispositions

On April 14, 2008,May 17, 2012, we sold a parcelcompleted the sale of landour Bedford Business Park properties located in Washington, DCBedford, Massachusetts for approximately $33.7$62.8 million in cash. Net cash proceeds totaled approximately $62.0 million, resulting in a gain on sale of approximately $36.9 million. We had previously entered into a development management agreement with the buyer to develop aBedford Business Park is comprised of two Office/Technical buildings and one Class A office property on the parcel totalingbuilding aggregating approximately 165,000470,000 net rentable square feet.

The servicer of the non-recourse mortgage loan on our Montvale Center property located in Gaithersburg, Maryland foreclosed on the property on January 31, 2012. As a result of the foreclosure, we recognized a gain on forgiveness of debt during the first quarter of 2012 totaling approximately $15.8 million, net of noncontrolling interests’ share of approximately $2.0 million. Due to a procedural error by the trustee, the foreclosure sale was subsequently dismissed by the applicable court prior to ratification. As a result, we have revised our involvement infinancial statements to properly reflect the construction of the project,property and related mortgage debt on our Consolidated Balance Sheet at December 31, 2012 and have reversed the gain on sale was deferredforgiveness of debt and has been recognized over the project construction period generally based onoperating activity from the percentageproperty within our consolidated statement of total project costs incurred to estimated total project costs. Duringoperations for the year ended December 31, 2010,2012. A subsequent foreclosure sale occurred on December 21, 2012 and ratification by the applicable court is pending. Once ratified, we completed construction of the project and recognized the remainingwill recognize a gain on sale totaling approximately $1.8 million. Weforgiveness of debt. These events have recognized a cumulative gainno impact on sale of approximately $23.4 million.

On May 5, 2010, we satisfied the requirements of our master lease agreement related to the 2006 sale of 280 Park Avenue in New York City, resulting in the recognition of the remaining deferred gain on sale of real estate totaling approximately $1.0 million. Following the satisfaction of the master lease agreement, the buyer terminated the property management and leasing agreement entered into at the time of the sale, resulting in the recognition of non-cash deferred management fees totaling approximately $12.2 million.cash flows.

Developments

On February 6, 2009, we announced that we were suspending construction on our 1,000,000 square foot project at 250 West 55th Street in New York City. During the year ended December 31, 2009, we recognized costs aggregating approximately $27.8 million related to the suspension of development, which amount included a $20.0 million contractual amount due pursuant to a lease agreement. During December 2009, we completed the construction of foundations and steel/deck to grade to facilitate a restart of construction in the future and as a result ceased interest capitalization on the project. On January 19, 2010, we paid $12.8 million related to the termination of the lease agreement. As a result, we recognized approximately $7.2 million of income during the year ended December 31, 2010.

On June 1, 2010, we placed in-service Weston Corporate Center, an approximately 356,000 net rentable square foot Class A office property located in Weston, Massachusetts. The property is 100% leased.

On October 20, 2010, we closed a transaction with a financial institution (the “HTC Investor”) related to the historic rehabilitation of the residential component of our Atlantic Wharf development in Boston, Massachusetts (the “residential project”). The residential project is expected to result in the development of approximately 86 units of residential rental apartments and approximately 10,000 square feet of retail space. Because, as a REIT, we may not take full advantage of available historic tax credits, we admitted the HTC Investor as a partner in the residential project. The HTC Investor has agreed to contribute an aggregate of approximately $14 million to the project in three installments in 2010 and 2011, subject to our achievement of certain conditions that include construction milestones and our compliance with the federal rehabilitation regulations. In exchange for its contribution, the HTC Investor will receive substantially all of the benefits derived from the tax credits.

As of December 31, 2010,2012, we had fivenine projects under construction comprised of threeeight office properties and twoone residential properties,property, which aggregate approximately 2.02.8 million square feet. We estimate the total investment to complete these projects, in the aggregate, to beis approximately $1.4$1.8 billion of which we had already invested approximately $1.1 billion as of December 31, 2010.2012. The investment through December 31, 20102012 and estimated total investment for our properties under construction as of December 31, 20102012 are detailed below (in thousands):

On January 3, 2012, we commenced the redevelopment of Two Patriots Park, a Class A office project with approximately 256,000 net rentable square feet located in Reston, Virginia. We will capitalize incremental costs during the redevelopment.

On April 30, 2012, we completed and fully placed in-service 510 Madison Avenue, a Class A office project with approximately 356,000 net rentable square feet located in New York City. As of December 31, 2012, the total investment was approximately $370.7 million with an estimated total investment upon completion of approximately $375.0 million.

On May 4, 2012, we completed and fully placed in-service One Patriots Park, a Class A office redevelopment project with approximately 268,000 net rentable square feet located in Reston, Virginia. As of December 31, 2012, the total investment was approximately $60.5 million with an estimated total investment upon completion of approximately $67.0 million.

On August 29, 2012, we acquired the development project located at 680 Folsom Street and 50 Hawthorne Street (which we refer to herein collectively as 680 Folsom Street) in San Francisco, California. When completed, the project will comprise approximately 522,000 net rentable square feet of Class A office and retail space. The project is approximately 85% pre-leased and as a result we have accounted for the acquisition as a business combination. The estimated project cost upon completion is approximately $340 million with initial occupancy expected in the first quarter of 2014. As part of the transaction, we also acquired the corner site of 690 Folsom Street, which is an adjacent parcel with a vacant 22,000 square foot, two-story structure that may be redeveloped in the future. The consideration paid by us to the seller consisted of approximately $62.2 million in cash and the issuance of 1,588,100 Series Four Preferred Units of limited partnership interest in our Operating Partnership. The Series Four Preferred Units are not convertible into or exchangeable for any common equity of our Operating Partnership or us, have a per unit liquidation preference of $50.00 and are entitled to receive quarterly distributions of $0.25 per unit (or an annual rate of 2.0%). In connection with the acquisition, we assumed a $170.0 million construction loan commitment and subsequently terminated the loan without ever drawing any amounts thereunder.

On December 14, 2012, we signed a 20-year lease with a law firm for approximately 246,000 net rentable square feet at 250 West 55^thStreet. 250 West 55^thStreet is an approximately 989,000 net rentable square foot office building under construction in midtown Manhattan. The development property is currently approximately 46% pre-leased with the remaining available office space in the upper portion of the tower.

On December 21, 2012, we signed a 20-year lease with a law firm for approximately 376,000 net rentable square feet at 601 Massachusetts Avenue, our planned approximately 478,000 net rentable square foot development project located in Washington, DC. Construction of the project, which is currently 100% leased and included in our in-service portfolio, is scheduled to commence in the second quarter of 2013, and building completion is expected to occur in the fourth quarter of 2015. The development property is currently approximately 79% pre-leased.

Secured Debt Transactions

On June 15, 2010,March 12, 2012, we used available cash to repay the mortgage loan collateralized by our Eight CambridgeBay Colony Corporate Center property located in Cambridge,Waltham, Massachusetts totaling approximately $22.6$143.9 million. The mortgage loanfinancing bore interest at a fixed rate of 7.73%6.53% per annum and was scheduled to mature on July 15, 2010.June 11, 2012. There was no prepayment penalty. We recognized a gain on early extinguishment of debt totaling approximately $0.9 million related to the acceleration of the remaining balance of the historical fair value adjustment, which was the result of purchase accounting.

On July 1, 2010, we used available cash to repay the mortgage loans collateralized by our 202, 206 & 214 Carnegie Center properties located in Princeton, New Jersey totaling approximately $55.8 million. The mortgage loans bore interest at a fixed rate of 8.13% per annum and were scheduled to mature on October 1, 2010. There were no prepayment penalties.

On August 1, 2010, we modified the mortgage loan collateralized by our Reservoir Place property located in Waltham, Massachusetts. The mortgage loan totaling $50.0 million bore interest at a variable rate equal to LIBOR plus 3.85% per annum and matures on July 30, 2014. The modification reduced the interest rate to a variable rate equal to Eurodollar plus 2.20% per annum. All other terms of the mortgage loan remain unchanged.

On September 24, 2010, in connection with the acquisition of 510 Madison Avenue in New York City, we assumed the mortgage loan totaling approximately $202.6 million and at closing caused the assignment of the mortgage to a new lender and subsequently increased the amount borrowed to $267.5 million. This amount is

fully secured by cash deposits included within “Cash Held in Escrows” in our Consolidated Balance Sheets. The mortgage financing bears interest at a variable rate equal to LIBOR plus 0.30% per annum and matures on February 24, 2012.

On October 1, 2010, we modified our construction loan facility collateralized by our Atlantic Wharf development project in Boston, Massachusetts. The construction loan facility bears interest at a variable rate equal to LIBOR plus 3.00% per annum and matures on April 21,2, 2012, with two, one-year extension options, subject to certain conditions. The modification consisted of releasing from collateral the residential component and ground floor retail included in the “Russia Building” and reducing the loan commitment from $215.0 million to $192.5 million. All other terms of the mortgage loan remain unchanged. We have not drawn any amounts under the facility.

On October 20, 2010, we used available cash to repay the mortgage loan collateralized by our South of MarketOne Freedom Square property located in Reston, Virginia totaling approximately $188.0$65.1 million. The mortgage financing bore interest at a fixed rate of 7.75% per annum and was scheduled to mature on June 30, 2012. There was no prepayment penalty. We recognized a gain on early extinguishment of debt totaling approximately $0.3 million related to the acceleration of the remaining balance of the historical fair value debt adjustment, which was the result of purchase accounting.

On August 29, 2012, in connection with our acquisition of the development project located at 680 Folsom Street in San Francisco, California, we assumed the construction loan commitment collateralized by the project (Refer to Note 3 of the Consolidated Financial Statements). The assumed construction loan commitment totaling $170.0 million bore interest at a variable rate equal to LIBOR plus 1.00%3.70% per annum and was scheduled to

mature on November 21, 2010. There was no prepayment penalty.May 30, 2015 with two, one-year extension options, subject to certain conditions. In addition, we assumed an interest rate derivative which capped the one-month LIBOR index rate at a maximum of 3.00% per annum on a notional amount up to $170.0 million and with an expiration date of May 30, 2015. On December 18, 2012, we terminated the construction loan commitment. On January 8, 2013, we terminated the interest rate derivative. We had not drawn any amounts under the facility.

On October 20, 2010,September 4, 2012, we used available cash to repay the mortgage loan collateralized by our Democracy TowerSumner Square property located in Reston, VirginiaWashington, DC totaling approximately $59.8$23.2 million. The mortgage loanfinancing bore interest at a variablefixed rate equal to LIBOR plus 1.75%of 7.35% per annum and was scheduled to mature on December 19, 2010. There was no prepayment penalty.

On NovemberSeptember 1, 2010, we used available cash to repay the mortgage loan collateralized by our 10 & 20 Burlington Mall Road property located in Burlington, Massachusetts and 91 Hartwell Avenue property located in Lexington, Massachusetts2013. We recognized a loss on early extinguishment of debt totaling approximately $32.8 million. The mortgage loan bore interest at a fixed rate of 7.25% per annum and was scheduled to mature on October 1, 2011. We paid$0.3 million, which included a prepayment penalty totaling approximately $0.3$0.2 million associated with the early repayment.

On November 1, 2010, we used available cash to repay the mortgage loan collateralized by our 1330 Connecticut Avenue property located in Washington, DC totaling approximately $45.0 million. The mortgage loan bore interest at a fixed rate of 7.58% per annum and was scheduled to mature on February 26, 2011. There was no prepayment penalty.

On December 23, 2010, we used available cash to repay the mortgage loan collateralized by our Wisconsin Place Office property totaling approximately $97.2 million. The mortgage loan bore interest at a variable rate equal to LIBOR plus 1.10% per annum and was scheduled to mature on January 29, 2011. There was no prepayment penalty.

On December 29, 2010,October 4, 2012, in connection with our acquisitionthe formation of a consolidated joint venture which owns and operates Fountain Square located in Reston, Virginia, the John Hancock Tower and Garage in Boston, Massachusetts, wejoint venture assumed the mortgage loan collateralized by the property totaling approximately $640.5 million.$211.3 million (Refer to Note 3 of the Consolidated Financial Statements). The assumed debt is a securitized senior mortgage loan that requires interest-only payments with a balloon payment due at maturity. Pursuant to the provisions of Accounting Standards Codification (“ASC”) 805, the assumed mortgage loan, which bears contractual interest at a fixed rate of 5.68%5.71% per annum and matures on January 6, 2017,October 11, 2016, was recorded at its fair value of approximately $663.4$234.4 million using an effective interest rate of 5.00%2.56% per annum. We have a 50% interest in the consolidated joint venture.

Unsecured Senior Notes

On April 19, 2010,June 11, 2012, our Operating Partnership completed a public offering of $700.0 million$1.0 billion in aggregate principal amount of its 5.625%3.850% senior unsecured notes due 2020.2023. The notes were priced at 99.891%99.779% of the principal amount to yield 5.708%an effective rate (including financing fees) of 3.954% to maturity. The notes will mature on February 1, 2023, unless earlier redeemed. The aggregate net proceeds tofrom the offering were approximately $989.4 million after deducting underwriting discounts and transaction expenses.

On August 24, 2012, our Operating Partnership after deducting underwriter discounts and offering expenses, were approximately $693.5 million. The notes mature on November 15, 2020, unless earlier redeemed. On April 7, 2010, in connection withused available cash to redeem the offering, we entered into

two treasury lock agreements to fix the 10-year U.S. Treasury rate (which was used as a reference security in pricing) at 3.873% per annum on notional amounts aggregating $350.0 million. We subsequently cash-settled the treasury lock agreements and received approximately $0.4 million, which amount will be recognized as a reduction to our interest expense over the term of the notes.

On November 18, 2010, our Operating Partnership completed a public offering of $850.0 million in aggregate principal amount of its 4.125% senior notes due 2021. The notes were priced at 99.26% of the principal amount to yield 4.289% to maturity. The aggregate net proceeds to our Operating Partnership, after deducting underwriter discounts and offering expenses, were approximately $836.9 million. The notes mature on May 15, 2021, unless earlier redeemed.

On December 12, 2010, our Operating Partnership completed the redemption of $700.0remaining $225.0 million in aggregate principal amount of its 6.25% senior notes due 2013. The redemption price was determined in accordance with the applicable indenture and wastotaled approximately $793.1$231.6 million. The redemption price included approximately $17.9$1.5 million of accrued and unpaid interest to, but not including, the redemption date. Excluding such accrued and unpaid interest, the redemption price was approximately 110.75%102.25% of the principal amount being redeemed. In addition,We recognized a loss on November 29, 2010, we entered into two treasury lock agreements to fix the yield on the U.S. Treasury issue used in determining the redemption price on notional amounts aggregating $700.0 million. On December 9, 2010, we cash-settled the treasury lock agreements and paidearly extinguishment of debt totaling approximately $2.1 million. As a result of$5.2 million, which amount included the payment of the redemption premium the settlement of the treasury locks and the write-off of deferred financing costs, we recognized an aggregate loss on early extinguishment of debt oftotaling approximately $79.3$5.1 million. Following the partial redemption, there is an aggregate of $225.0 million of these notes outstanding.

Unsecured Exchangeable Senior Notes

DuringOn January 10, 2012, we announced that holders of the year ended December 31, 2010,2.875% Exchangeable Senior Notes due 2037 (the “Notes”) issued by our Operating Partnership had the right to surrender their Notes for purchase by our Operating Partnership (the “Put Right”) on February 15, 2012. The opportunity to exercise the Put Right expired on February 8, 2012. On January 10, 2012, we also announced that our Operating Partnership issued a notice of redemption to the holders of the Notes to redeem, on February 20, 2012 (the “Redemption Date”), all of the Notes outstanding on the Redemption Date. In connection with the redemption, holders of the Notes had the right to exchange their Notes on or prior to February 16, 2012. Notes with respect to which the Put Right was not exercised (or with respect to which the Put Right was exercised and subsequently withdrawn prior to the withdrawal deadline) and that were not surrendered for exchange on or prior to February 16, 2012, were redeemed by our Operating Partnership on the Redemption Date at a redemption price equal to 100% of the principal amount of the Notes plus accrued and unpaid interest thereon to, but excluding, the Redemption Date. Holders of an aggregate of $242,735,000 of the Notes exercised the Put Right and our Operating Partnership repurchased approximately $236.3 million aggregatesuch Notes on February 15, 2012. On February 20, 2012, our Operating Partnership redeemed the remaining $333,459,000 of outstanding Notes at a redemption price equal to 100% of the principal amount of its 2.875% exchangeable senior notes due 2037, which the holders may require our Operating Partnership to repurchase in February 2012, for approximately $236.6 million. The repurchased notes had an aggregate allocated liabilityNotes plus accrued and equity value of approximately $225.7 million and $0.4 million, respectively, at the time of repurchase resulting in the recognition of a loss on early extinguishment of debt of approximately $10.5 million during the year ended December 31, 2010. There remains an aggregate of approximately $626.2 million of these notes outstanding.unpaid interest thereon.

Unsecured Line of Credit

Effective as of August 3, 2010, the maturity date under our Operating Partnership’s $1.0 billion unsecured line of credit was extended to August 3, 2011. All other terms of the unsecured line of credit remain unchanged.

Equity Transactions

On June 2, 2011, we established a new “at the market” (“ATM”) stock offering program through which we may sell from time to time up to an aggregate of $600.0 million of our common stock through sales agents over a three-year period. During the year ended December 31, 2012, we issued an aggregate of 2,347,500 shares of common stock under this ATM stock offering program for gross proceeds of approximately $249.8 million and net proceeds of approximately $247.0 million. As of December 31, 2012, approximately $305.3 million remained available for issuance under this ATM program.

During the year ended December 31, 2010,2012, we acquired an aggregate of 591,9001,110,660 common units of limited partnership interest, including 99,139544,729 common units issued upon the conversion of LTIP units and 153,604 issued upon the conversion of Series Two preferred units, presented by the holders for redemption, in exchange for an equal number of shares of common stock. During the year ended December 31, 2010,2012, we issued 638,95722,823 shares of common stock as a result of stock options being exercised.

Noncontrolling interests in property partnerships

On December 23, 2010, we acquired the outside member’s 33.3% equity interest in our consolidated joint venture entity that owns the Wisconsin Place Office property located in Chevy Chase, Maryland for cash of approximately $25.5 million. The acquisition was accounted for as an equity transaction. The difference between the purchase price and the carrying value of the outside member’s equity interest, totaling approximately $19.1 million, reduced additional paid-in capital in our Consolidated Balance Sheets.

Investments in Unconsolidated Joint Ventures

On March 1, 2010, a joint venture in which we have a 60% interest refinanced at maturity its mortgage loan collateralized by 125 West 55th Street located in New York City. The mortgage loan totaling $200.0 million bore interest at a fixed rate of 5.75% per annum. The new mortgage loan totaling $207.0 million bears interest at a fixed rate of 6.09% per annum and was scheduled to mature on March 10, 2015. On July 23, 2010, the joint venture modified the mortgage loan by extending the maturity date of the loan to March 10, 2020. All other terms of the mortgage loan remain unchanged. In connection with the new mortgage loan, we have guaranteed the joint venture’s obligation to fund an escrow related to certain lease rollover costs in lieu of an initial cash deposit for the full amount. The maximum funding obligation under the guarantee was $21.3 million. At closing, the joint venture funded a $10.0 million cash deposit into the escrow account and the remaining $11.3 million will be further reduced with scheduled monthly deposits into the escrow account from operating cash flows. As of December 31, 2010, the maximum funding obligation under the guarantee was approximately $7.2 million. We earn a fee from the joint venture for providing the guarantee and have an agreement with the outside partners to reimburse the joint venture for their share of any payments made under the guarantee. In addition, on February 25, 2010, the joint venture repaid outstanding mezzanine loans totaling $63.5 million utilizing available cash and cash contributions from the joint venture’s partners on a pro rata basis. The mezzanine loans bore interest at a weighted-average fixed rate of approximately 7.81% per annum and were scheduled to mature on March 1, 2010.

On April 1, 2010, we acquired a 30% interest in a joint venture entity that owns 500 North Capitol Street, NW located in Washington, DC. 500 North Capitol Street is an approximately 176,000 net rentable square foot office property that is fully-leased to a single tenant through March 25, 2011. The joint venture currently intends to remove the property from service and redevelop the property following the lease expiration. On April 1, 2010, the joint venture entity refinanced at maturity the mortgage loan collateralized by the property totaling approximately $26.8 million. The new mortgage loan totaling $22.0 million bears interest at a variable rate equal to the greater of (1) the prime rate, as defined in the loan agreement, or (2) 5.75% per annum. The loan currently bears interest at 5.75% per annum and matures on March 31, 2013. Our investment in the joint venture totaling approximately $1.9 million was financed with cash contributions to the venture totaling approximately $1.4 million and the issuance to the seller of 5,906 OP Units.

On April 9, 2010, a joint venture in which we have a 60% interest refinanced its mortgage loan collateralized by Two Grand Central Tower located in New York City. The previous mortgage loan totaling $190.0 million bore interest at a fixed rate of 5.10% per annum and was scheduled to mature on July 11, 2010. The new mortgage loan totaling $180.0 million bears interest at a fixed rate of 6.00% per annum and matures on April 10, 2015. In connection with the refinancing, the joint venture repaid $10.0 million of the previous mortgage loan utilizing cash contributions from the joint venture’s partners on a pro rata basis.

On April 16, 2010, a joint venture in which we have a 51% interest refinanced its mortgage loan collateralized by Metropolitan Square located in Washington, DC. The previous mortgage loan totaling approximately $123.6 million bore interest at a fixed rate of 8.23% per annum and was scheduled to mature on May 1, 2010. The new mortgage loan totaling $175.0 million bears interest at a fixed rate of 5.75% per annum and matures on May 5, 2020. On April 26, 2010, the joint venture distributed excess loan proceeds to the partners totaling approximately $49.0 million, of which our share was approximately $25.0 million.

On June 15, 2010,2012, a joint venture in which we have a 50% interest repaidpartially placed in-service Annapolis Junction Building Six, a Class A office property with approximately 120,000 net rentable square feet located in Annapolis, Maryland.

On September 27, 2012, our Value-Added Fund completed the sale of its 300 Billerica Road property located in Chelmsford, Massachusetts for approximately $12.2 million, including the assumption by the buyer of $7.5 million of mortgage loan collateralized by land parcels at its site at Eighth Avenue and 46th Street in New York City utilizingindebtedness. 300 Billerica Road is an approximately 111,000 net rentable square foot office building. Net cash contributionsproceeds totaled approximately $4.3 million, of which our share was approximately $2.8 million, after the payment of transaction costs. Our share of the net proceeds included approximately $2.4 million resulting from the joint venture’s partnersValue-Added Fund’s repayment of a loan from our Operating Partnership. The Value-Added Fund recognized a gain on a pro rata basis. In addition, the joint venture completed an exchangesale of land parcels with a third party and received land parcels and development rights valued atreal estate totaling approximately $6.4$1.0 million, in exchange for a land parcel valued atof which our share totaled approximately $5.4$0.2 million and cashis included within income from unconsolidated joint ventures in our consolidated statements of approximately $1.0 million.operations.

On September 12, 2010,October 1, 2012, a joint venture in which we have a 50%30% interest exercised its right to extend the maturity date of its mortgage loan collateralized by Annapolis Junction located in Annapolis, Maryland. The mortgage loan totaling $42.7 million now matures on September 12, 2011 and bears interest atpartially placed in-service 500 North Capitol Street, NW, a variable rate equal to LIBOR plus 1.00% per annum. The mortgage loan includes an additional one-year extension option, subject to certain conditions. All other terms of the mortgage loan remain unchanged.

On September 20, 2010, a joint venture in which we have a 50% interest refinanced its mortgage loan collateralized by Market Square NorthClass A office redevelopment project with approximately 232,000 net rentable square feet located in Washington, DC. The previous mortgage loan totaling approximately $81.1 million bore interest at a fixed rate of 7.70% per annum and was scheduled to mature on December 19, 2010. The new mortgage loan totaling $130.0 million bears interest at a fixed rate of 4.85% per annum and matures on October 1, 2020. property is currently 82% leased.

��

On October 22, 2010,19, 2012, we formed a joint venture with an affiliate of Hines to pursue the acquisition of land in San Francisco, California which could support a 61-story, 1.4 million square foot office tower known as Transbay Tower. The purchase price is approximately $190.0 million, and the acquisition is expected to close in the first quarter of 2013. We have a 50% interest in the joint venture. We have provided a non-refundable deposit for the land purchase in the form of a letter of credit totaling $5.0 million. There can be no assurance that the acquisition of the land will be consummated on the terms currently contemplated or at all. On February 7, 2013, the affiliate of Hines issued a notice that it has elected under the joint venture distributed excess loan proceedsagreement to reduce its nominal ownership interest in the venture from 50% to 5%. On February 26, 2013, we issued a notice electing to proceed with the venture on that basis. As a result, we have a 95% nominal interest in, and expect to consolidate, the joint venture. Refer to Note 20 to the partners totaling approximately $40.8 million, of which our share was approximately $20.4 million.Consolidated Financial Statements.

On OctoberNovember 21, 2010,2012, our Value-Added Fund conveyed the fee simple title to its Onepartner in our Annapolis Junction joint venture contributed a parcel of land and Two Circle Star Way propertiesimprovements and paid $3.8 million to the lender in satisfactionwe contributed cash of its outstanding obligations under the existing mortgage loan and guarantee. Our Value-Added Fund recognized a net gain on early extinguishment of debt totaling approximately $17.9$5.4 million. We had previously recognized impairment losses on our investmenthave a 50% interest in the Value-Added Fund.this joint venture. The mortgage loan had an outstanding principal amountventure has commenced construction of $42.0 million, bore interest atAnnapolis Junction Building Seven, which when completed will consist of a fixed rate of 6.57% per annumClass A office property with approximately 125,000 net rentable square feet located in Annapolis, Maryland.

Stock Option and was scheduled to mature on September 1, 2013. The Value-Added Fund had guaranteed the payment of (1) an aggregate of approximately $5.0 million of unfunded tenant improvement costs and leasing commissions and (2) one year of real estate taxes. We had an effective ownership interest of 25% in the One and Two Circle Star Way properties.Incentive Plan

On December 23, 2010, we soldJanuary 25, 2012, our 5.0% equity interest inCompensation Committee approved outperformance awards under our unconsolidated joint venture entity that owned the retail portion of the Wisconsin Place mixed-use property for approximately $1.4 million of cash, resulting in the recognitionStock Option and Incentive Plan to our officers and employees. These awards (the “2012 OPP Awards”) are part of a gainbroad-based, long-term incentive compensation program designed to provide our management team with the potential to earn equity awards subject to us “outperforming” and creating shareholder value in a pay-for-performance structure. Recipients of 2012 OPP Awards will share in a maximum outperformance pool of $40.0 million if the total return to shareholders, including both share appreciation and dividends, exceeds absolute and relative hurdles over a three-year measurement period from February 7, 2012 to February 6, 2015. Earned awards are subject to two-years of time-based vesting after the performance measurement date. Under the Financial Accounting Standards Board’s Accounting Standards Codification (“ASC”) 718 “Compensation—Stock Compensation,” the 2012 OPP Awards have an aggregate value of approximately $0.6$7.7 million, which amount is included within income (loss) from unconsolidated joint ventures withinwill be amortized into earnings over the five-year plan period under the graded vesting method.

Executive Resignation

On February 29, 2012, E. Mitchell Norville resigned as our Consolidated StatementsExecutive Vice President, Chief Operating Officer. In connection with his resignation, Mr. Norville entered into a separation agreement with us. We recognized approximately $4.5 million of Operations.

Business and Growth Strategies

Business Strategy

Our primary business objective is to maximize return on investment so as to provide our investors with the greatest possible total return. Our strategy to achieve this objective is:

Growth Strategies

External Growth

We believe that our development experience and our organizational depth position us to continue to selectively develop a range of property types, including low-rise suburban office properties, high-rise urban developments, mixed-use developments (including residential) and research and laboratory space, within budget and on schedule. We believe we are also well positioned to achieve external growth through acquisitions. Other factors that contribute to our competitive position include:

Opportunities to execute our external growth strategy fall into three categories:

In the past, we have been particularly successful at acquiring sites or options to purchase sites that need governmental approvals for development. Because of our development expertise, knowledge of the governmental approval process and reputation for quality development with local government regulatory bodies, we generally have been able to secure the permits necessary to allow development and to profit from the resulting increase in land value. We seek complex projects where we can add value through the efforts of our experienced and skilled management team leading to attractive returns on investment.

Our strong regional relationships and recognized development expertise have enabled us to capitalize on unique build-to-suit opportunities. We intend to seek and expect to continue to be presented with such opportunities in the near term allowing us to earn relatively significant returns on these development opportunities through multiple business cycles.

•

Acquisition of underperforming assets and portfolios of assets. We believe that because of our in-depth market knowledge and development experience in each of our markets, our national reputation with brokers, financial institutions and others involved in the real estate market and our access to competitively-priced capital, we are well-positioned to identify and acquire existing, underperforming properties for competitive prices and to add significant additional value to such properties through our effective marketing strategies, repositioning/redevelopment expertise and a responsive property management program. We have developed this strategy and program for our existing portfolio, where we provide high-quality property management services using our own employees in order to encourage tenants to renew, expand and relocate in our properties. We are able to achieve speed and transaction cost efficiency in replacing departing tenants through the use of in-house and third-party vendors’ services for marketing, including calls and presentations to prospective tenants, print advertisements, lease negotiation and construction of tenant improvements. Our tenants benefit from cost efficiencies produced by our experienced work force, which is attentive to preventive maintenance and energy management.

Internal Growth

We believe that opportunities will exist to increase cash flow from our existing properties because they are of high quality and in desirable locations within markets where, in general, the creation of new supply is limited by the lack of available sites and the difficulty of obtaining the necessary approvals for development on vacant land and financing. Our strategy for maximizing the benefits from these opportunities is three-fold: (1) to provide high-quality property management services using our employees in order to encourage tenants to renew, expand and relocate in our properties, (2) to achieve speed and transaction cost efficiency in replacing departing tenants through the use of in-house services for marketing, lease negotiation and construction of tenant improvements and (3) to work with new or existing tenants with space expansion or contraction needs maximizing the cash flow from our assets. We expect to continue our internal growth as a result of our ability to:

We had an

The average lease term of 7.1our in-place leases, including unconsolidated joint ventures, was approximately 6.9 years at December 31, 20102012 and we continue to cultivate long-term leasing relationships with a diverse base of high-quality, financially stable tenants. Based on leases in place at December 31, 2010,2012, leases with respect to 6.9%approximately 4.0% of the total square feet in our portfolio (excluding 601 Massachusetts Avenue, which will be removed from service for redevelopment in 2013), including unconsolidated joint ventures, will expire in calendar year 2011.2013.

Policies with Respect to Certain Activities

The discussion below sets forth certain additional information regarding our investment, financing and other policies. These policies have been determined by our Board of Directors and, in general, may be amended or revised from time to time by our Board of Directors.

Investment Policies

Investments in Real Estate or Interests in Real Estate

Our investment objectives are to provide quarterly cash dividends to our securityholders and to achieve long-term capital appreciation through increases in the value of Boston Properties, Inc. We have not established a specific policy regarding the relative priority of these investment objectives.

We expect to continue to pursue our investment objectives primarily through the ownership of our current properties, development projects and other acquired properties. We currently intend to continue to invest primarily in developments of properties and acquisitions of existing improved properties or properties in need of redevelopment, and acquisitions of land that we believe have development potential, primarily in our markets—existing markets of Boston, Washington, DC, midtown Manhattan,New York, Princeton, San Francisco and Princeton, NJ.Washington, DC, but also potentially in new markets. Future investment or development activities will not be limited to a specified percentage of our assets. We intend to engage in such future investment or development activities in a manner that is consistent with the maintenance of our status as a REIT for federal income tax purposes. In addition, we may purchase or lease income-producing commercial and other types of properties for long-term investment, expand and improve the real estate presently owned or other properties purchased, or sell such real estate properties, in whole or in part, when circumstances warrant. We do not have a policy that restricts the amount or percentage of assets that will be invested in any specific property, however, our investments may be restricted by our debt covenants.

We may also continue to participate with third parties in property ownership, through joint ventures or other types of co-ownership, including third parties with expertise in mixed-use opportunities. These investments may permit us to own interests in larger assets without unduly restricting diversification and, therefore, add flexibility in structuring our portfolio.

Equity investments may be subject to existing mortgage financing and other indebtedness or such financing or indebtedness as may be incurred in connection with acquiring or refinancing these investments. Debt service on such financing or indebtedness will have a priority over any distributions with respect to our common stock. Investments are also subject to our policy not to be treated as an investment company under the Investment Company Act of 1940, as amended (the “1940 Act”).

Investments in Real Estate Mortgages

While our current portfolio consists primarily of, and our business objectives emphasize, equity investments in commercial real estate, we may, at the discretion of the Board of Directors, invest in mortgages and other types of real estate interests consistent with our qualification as a REIT. Investments in real estate mortgages run the risk that one or more borrowers may default under such mortgages and that the collateral securing such mortgages may not be sufficient to enable us to recoup our full investment. Although we currently do not have any investments in mortgages or deeds of trust, weWe may invest in participating, convertible or traditional mortgages if we conclude that we may benefit from the cash flow, or any appreciation in value of the property or as an entrance to the fee ownership.

Securities of or Interests in Entities Primarily Engaged in Real Estate Activities

Subject to the percentage of ownership limitations and gross income and asset tests necessary for our REIT qualification, we also may invest in securities of other REITs, other entities engaged in real estate activities or securities of other issuers, including for the purpose of exercising control over such entities.

Dispositions

Our decision to dispose of properties areis based upon the periodic review of our portfolio and the determination by the Board of Directors that such action would be in our best interests. Any decision to dispose of a property will be authorized by the Board of Directors or a committee thereof. Some holders of limited partnership interests in BPLP, including Mortimer B. Zuckerman, and the estate of Edward H. Linde, could incur adverse tax consequences upon the sale of certain of our properties that differ from the tax consequences to us. Consequently, holders of limited partnership interests in BPLP may have different objectives regarding the appropriate pricing and timing of any such sale. Such different tax treatment derives in most cases from the fact that we acquired these properties in exchange for partnership interests in contribution transactions structured to allow the prior owners to defer taxable gain. Generally this deferral continues so long as we do not dispose of the properties in a taxable transaction. Unless a sale by us of these properties is structured as a like-kind exchange under Section 1031 of the Internal Revenue Code or in a manner that otherwise allows deferral to continue, recognition of the deferred tax gain allocable to these prior owners is generally triggered by a sale. Some of our assets are subject to tax protection agreements, which may limit our ability to dispose of the assets or require us to pay damages to the prior owners in the event of a taxable sale.

Financing Policies

The agreement of limited partnership of BPLP and our certificate of incorporation and bylaws do not limit the amount or percentage of indebtedness that we may incur. We do not have a policy limiting the amount of indebtedness that we may incur. However, our mortgages, credit facilities and unsecured debt securities contain customary restrictions, requirements and other limitations on our ability to incur indebtedness. We have not established any limit on the number or amount of mortgages that may be placed on any single property or on our portfolio as a whole.

Our Board of Directors will consider a number of factors when evaluating our level of indebtedness and when making decisions regarding the incurrence of indebtedness, including the purchase price of properties to be acquired with debt financing, the estimated market value of our properties upon refinancing, the entering into agreements such as interest rate swaps, caps, floors and other interest rate hedging contracts and the ability of particular properties and BPLP as a whole to generate cash flow to cover expected debt service.

Policies with Respect to Other Activities

As the sole general partner of BPLP, we have the authority to issue additional common and preferred units of limited partnership interest of BPLP. We have in the past, and may in the future, issue common or preferred units of limited partnership interest of BPLP to persons who contribute their direct or indirect interests in properties to us in exchange for such common or preferred units of limited partnership interest in BPLP. We have not engaged in trading, underwriting or agency distribution or sale of securities of issuers other than BPLP and we do not intend to do so. At all times, we intend to make investments in such a manner as to maintain our qualification as a REIT, unless because of circumstances or changes in the Internal Revenue Code of 1986, as amended (or the Treasury Regulations), our Board of Directors determines that it is no longer in our best interest to qualify as a REIT. We may make loans to third parties, including, without limitation, to joint ventures in which we participate or in connection with the disposition of a property. We intend to make investments in such a way that we will not be treated as an investment company under the 1940 Act. Our policies with respect to these and other activities may be reviewed and modified or amended from time to time by the Board of Directors.

Sustainability

As one of the largest owners and developers of office properties in the United States, we actively work to promote our growth and operations in a sustainable and responsible manner across our five regions. We focus our sustainability initiatives on the design and construction of our new developments, the operation of our existing

buildings and our internal corporate practices. Our sustainability initiatives are centered on energy efficiency, waste reduction and water preservation, as well as making a positive impact on the communities in which we conduct business. Through these efforts we demonstrate that operating and developing commercial real estate can be conducted with a conscious regard for the environment while mutually benefiting our tenants, investors, employees and the communities in which we operate. In November 2010, we launched a new pageWe provide disclosure on our website to increase the transparency of our sustainability program.program, which we periodically update with current or additional information. You may access our sustainability report on our website at http://www.bostonproperties.com under the heading “Sustainability.”

Competition

We compete in the leasing of office, retail and residential space with a considerable number of other real estate companies, some of which may have greater marketing and financial resources than are available to us. In addition, our hotel property competes for guests with other hotels, some of which may have greater marketing and financial resources than are available to us and to the manager of our one hotel, Marriott International, Inc.

Principal factors of competition in our primary business of owning, acquiring and developing office properties are the quality of properties, leasing terms (including rent and other charges and allowances for tenant improvements), attractiveness and convenience of location, the quality and breadth of tenant services provided, and reputation as an owner and operator of quality office properties in the relevant market. Additionally, our ability to compete depends upon, among other factors, trends of the national and local economies, investment alternatives, financial condition and operating results of current and prospective tenants, availability and cost of capital, construction and renovation costs, taxes, utilities, governmental regulations, legislation and population trends.

In addition, although not part of our core strategy, we are currently developing one residential property and operate two residential properties that are incidental to our office developments and may in the future decide to acquire or develop additional residential properties. As an owner and operator of apartments, we will also face competition for prospective residents from other operators whose properties may be perceived to offer a better location or better amenities or whose rent may be perceived as a better value given the quality, location and amenities that the resident seeks. We will also compete against condominiums and single-family homes that are for sale or rent. Because we have limited experience with residential properties, we expect to retain third parties to manage our residential properties.

Our Hotel Property

We operate our hotel property through a taxable REIT subsidiary. The taxable REIT subsidiary, a wholly-owned subsidiary of BPLP, is the lessee pursuant to a lease for the hotel property. As lessor, BPLP is entitled to a percentage of gross receipts from the hotel property. The hotel lease allows all the economic benefits of ownership to flow to us. Marriott International, Inc. continues to manage the hotel property under the Marriott name and under terms of the existing management agreements. Marriott has been engaged under a separate long-term incentive management agreement to operate and manage the hotel on behalf of the taxable REIT subsidiary. In connection with these arrangements, Marriott has agreed to operate and maintain our hotel in accordance with its system-wide standard for comparable hotels and to provide the hotel with the benefits of its central reservation system and other chain-wide programs and services. Under a management agreement for the hotel, Marriott acts as the taxable REIT subsidiary’s agent to supervise, direct and control the management and operation of the hotel and receives as compensation base management fees that are calculated as a percentage of the hotel’s gross revenues, and supplemental incentive fees if the hotel exceeds negotiated profitability breakpoints. In addition, the taxable REIT subsidiary compensates Marriott, on the basis of a formula applied to the hotel’s gross revenues, for certain system-wide services provided by Marriott, including central reservations, marketing and training. During 2010, 20092012, 2011 and 2008,2010, Marriott received an aggregate of approximately $2.2$2.0 million, $1.5$2.5 million and $3.0$2.2 million, respectively, from our taxable REIT subsidiary.

Seasonality

Our hotel property traditionally has experienced significant seasonality in its operating income, with the percentage of net operating income by quarter over the year ended December 31, 20102012 shown below.

Corporate Governance

Boston Properties is currently governed by a ten member Board of Directors, which is divided into three classes (Class I, Class II and Class III). OurDirectors. The current members of our Board of Directors is currently comprised of three Class I directors (Mortimerare Mortimer B. Zuckerman, Zoë Baird Budinger, Carol B. Einiger, and Dr. Jacob A. Frenkel), four Class II directors (Lawrence S. Bacow, Zoë Baird, Alan J. Patricof and Martin Turchin) and three Class III directors (DouglasFrenkel, Joel I. Klein, Douglas T. Linde, Matthew J. Lustig, Alan J. Patricof, Martin Turchin and David A. Twardock). The terms of our current Class I, Class II and Class III directors expire at the annual meetings of stockholders to be held in 2013, 2011 and 2012, respectively.Twardock.

At the 2010 annual meeting of stockholders, our stockholders approved an amendment to our Amended and Restated Certificate of Incorporation (the “Charter”) that will, among other things, destagger the Board of Directors and provideprovides for the annual election of directors. As a result, commencing with the class ofall directors standing for election at the 2011 annual meeting of stockholders our directors whose terms expire willnow stand for election for one-year terms expiring at the next succeeding annual meeting of stockholders.

On September 11, 2012, Lawrence S. Bacow resigned as our Director to devote more time to his other interests. Mr. Bacow has confirmed to our Board of Directors elected priorthat his resignation was not due to the 2011 annual meeting of stockholders will continuea disagreement with us on any matter relating to serve their full three-year terms.our operations, policies or practices.

On January 20, 2011, Matthew J. Lustig24, 2013, Joel I. Klein was appointed as a Class III director to serve until the 20122013 annual meeting of stockholders. The Board of Directors also appointed Mr. Klein to its Nominating and Corporate Governance Committee.

Our Board of Directors has Audit, Compensation and Nominating and Corporate Governance Committees. The membership of each of these committees is described below.

X=Committee member, *=Chair

Governance” and subheading “Code of Conduct and Ethics.” We intend to disclose on this website any amendment to, or waiver of, any provision of this Code applicable to our directors and executive officers that would otherwise be required to be disclosed under the rules of the SEC or the New York Stock Exchange.

New U.S. Income Tax Legislation

Pursuant to recently enacted legislation, as of January 1, 2013, (1) the maximum tax rate on “qualified dividend income” for individuals is 20%, (2) the maximum tax rate on long-term capital gain for individuals is 20%, (3) the highest marginal individual income tax rate is 39.6%, and (4) the backup withholding rate remains at 28%. Such legislation also temporarily (through 2013) reduces to five years the ten-year recognition period applicable to gain recognized on the disposition of an asset acquired from a C corporation in a carryover basis transaction, as well as makes permanent certain federal income tax provisions that were scheduled to expire on December 31, 2012.

In addition, the effective date for U.S. withholding taxes that may apply, in certain circumstances, under the Foreign Account Tax Compliance Act, on the gross proceeds from the sale of our stock or notes or the Operating Partnership’s notes has been extended from payments after December 31, 2014 to payments after December 31, 2016.

Item 1A.

Risk Factors.

Set forth below are the risks that we believe are material to our investors. We refer to the shares of our common stock and the units of limited partnership interest in BPLP together as our “securities,” and the investors who own shares or units, or both, as our “securityholders.” This section contains forward-looking statements. You should refer to the explanation of the qualifications and limitations on forward-looking statements beginning on page 48.

Our performance and value are subject to risks associated with our real estate assets and with the real estate industry.

Our economic performance and the value of our real estate assets, and consequently the value of our securities, are subject to the risk that if our office and hotel properties do not generate revenues sufficient to meet our operating expenses, including debt service and capital expenditures, our cash flow and ability to pay distributions to our securityholders will be adversely affected. The following factors, among others, may adversely affect the income generated by our office and hotel properties:

We are dependent upon the economic climates of our markets—Boston, Washington, DC, midtown Manhattan,New York, Princeton, San Francisco and Princeton, NJ.Washington, DC.

Substantially all of our revenue is derived from properties located in five markets: Boston, Washington, DC, midtown Manhattan,New York, Princeton, San Francisco and Princeton, NJ.Washington, DC. A downturn in the economies of these markets, or the impact that a downturn in the overall national economy may have upon these economies, could result in reduced demand for office space. Because our portfolio consists primarily of office buildings (as compared to a more diversified real estate portfolio), a decrease in demand for office space in turn could adversely affect our results of operations. Additionally, there are submarkets within our markets that are dependent upon a limited number of industries. For example, in our Washington, DC market we focus on leasing office properties to governmental agencies and contractors, as well as legal firms. A reduction in spending by the federal government, either resulting from sequestration or the annual budgetary process, could result in reduced demand for office space and adversely effect our results of operations, In addition, in our midtown ManhattanNew York market we have historically leased properties to financial, legal and other professional firms. A significant downturn in one or more of these sectors could adversely affect our results of operations.

In addition, a significant economic downturn over a period of time could result in an event or change in circumstances that results in an impairment in the value of our properties.properties or our investments in unconsolidated joint ventures. An impairment loss is recognized if the carrying amount of the asset (1) is not recoverable over its expected holding period and (2) exceeds its fair value. There can be no assurance that we will not take charges in the future related to the impairment of our assets.assets or investments. Any future impairment could have a material adverse effect on our results of operations in the period in which the charge is taken.

Our investment in property development may be more costly than anticipated.

We intend to continue to develop and substantially renovate office and residential properties. Our current and future development and construction activities may be exposed to the following risks:

Investment returns from our developed properties may be lowerless than anticipated.

Our developed properties may be exposed to the following risks:

We face risks associated with the development of mixed-use commercial properties.

We operate, are currently developing, and may in the future develop, properties either alone or through joint ventures with other persons that are known as “mixed-use” developments. This means that in addition to the development of office space, the project may also include space for residential, retail, hotel or other commercial purposes. We have limited experience in developing and managing non-office and non-retail real estate. As a result, if a development project includes a non-office or non-retail use, we may seek to develop that component ourselves, sell the rights to that component to a third-party developer with experience in that use or we may seek

to partner with such a developer. If we do not sell the rights or partner with such a developer, or if we choose to develop the other component ourselves, we would be exposed not only to those risks typically associated with the development of

commercial real estate generally, but also to specific risks associated with the development and ownership of non-office and non-retail real estate. In addition, even if we sell the rights to develop the other component or elect to participate in the development through a joint venture, we may be exposed to the risks associated with the failure of the other party to complete the development as expected. These include the risk that the other party would default on its obligations necessitating that we complete the other component ourselves (including providing any necessary financing). In the case of residential properties, these risks include competition for prospective residents from other operators whose properties may be perceived to offer a better location or better amenities or whose rent may be perceived as a better value given the quality, location and amenities that the resident seeks. We will also compete against condominiums and single-family homes that are for sale or rent. Because we have limited experience with residential properties, we expect to retain third parties to manage our residential properties. If we decide to not sell or participate in a joint venture and instead hire a third party manager, we would be dependent on them and their key personnel who provide services to us and we may not find a suitable replacement if the management agreement is terminated, or if key personnel leave or otherwise become unavailable to us.

We face risks associated with the use of debt to fund acquisitions and developments, including refinancing risk.

We are subject to the risks normally associated with debt financing, including the risk that our cash flow will be insufficient to meet required payments of principal and interest. We anticipate that only a small portion of the principal of our debt will be repaid prior to maturity. Therefore, we are likely to need to refinance at least a portion of our outstanding debt as it matures. There is a risk that we may not be able to refinance existing debt or that the terms of any refinancing will not be as favorable as the terms of our existing debt. If principal payments due at maturity cannot be refinanced, extended or repaid with proceeds from other sources, such as new equity capital, our cash flow may not be sufficient to repay all maturing debt in years when significant “balloon” payments come due. In addition, we may rely on debt to fund a portion of our new investments such as our acquisition and development activity. There is a risk that we may be unable to finance these activities on favorable terms or at all. This risk is currently heightened because of tightened underwriting standards and increased credit risk premiums. These conditions, which increase the cost and reduce the availability of debt, may continue or worsen in the future.

We have agreements with a number of limited partners of BPLP who contributed properties in exchange for partnership interests that require BPLP to maintain for specified periods of time secured debt on certain of our assets and/or allocate partnership debt to such limited partners to enable them to continue to defer recognition of their taxable gain with respect to the contributed property. These tax protection and debt allocation agreements may restrict our ability to repay or refinance debt.

Adverse economic and geopolitical conditions and dislocations in the credit markets could have a material adverse effect on our results of operations, financial condition and ability to pay distributions to you.

Our business may be affected by market and economic challenges experienced by the U.S. economy or real estate industry as a whole, or by the local economic conditions in the markets in which our properties are located, including the continuing impact of high unemployment, and constrained credit.by international economic conditions. These current conditions, or similar conditions existing in the future, may adversely affect our results of operations, financial condition and ability to pay distributions as a result of the following, among other potential consequences:

An increase in interest rates would increase our interest costs on variable rate debt and could adversely impact our ability to refinance existing debt or sell assets on favorable terms or at all.

As of February 18, 2011,21, 2013, we had approximately $317.5 million ofno indebtedness, excluding our unconsolidated joint ventures, that bears interest at variable rates, andbut we may incur more of such indebtedness in the future. If interest rates increase, then so willwould the interest costs on our unhedged variable rate debt, which could adversely affect our cash flow and our ability to pay principal and interest on our debt and our ability to make distributions to our securityholders. Further, rising interest rates could limit our ability to refinance existing debt when it matures or significantly increase our future interest expense. From time to time, we enter into interest rate swap agreements and other interest rate hedging contracts, including swaps, caps and floors. While these agreements are intended to lessen the impact of rising interest rates on us, they also expose us to the risk that the other parties to the agreements will not perform, we could incur significant costs associated with the settlement of the agreements, the agreements will be unenforceable and the underlying transactions will fail to qualify as highly-effective cash flow hedges under guidance included in ASC 815 “Derivatives and Hedging” (formerly known as SFAS No. 133, “Accounting for Derivative Instruments and Hedging Activities, as amended”). In addition, an increase in interest rates could decrease the amounts third-parties are willing to pay for our assets, thereby limiting our ability to change our portfolio promptly in response to changes in economic or other conditions.

Covenants in our debt agreements could adversely affect our financial condition.

The mortgages on our properties contain customary covenants such as those that limit our ability, without the prior consent of the lender, to further mortgage the applicable property or to discontinue insurance coverage. Our unsecured credit facility, unsecured debt securities and certain secured loans contain customary restrictions, requirements and other limitations on our ability to incur indebtedness, including total debt to asset ratios, secured debt to total asset ratios, debt service coverage ratios and minimum ratios of unencumbered assets to unsecured debt, which we must maintain. Our continued ability to borrow under our credit facilities is subject to compliance with our financial and other covenants. In addition, our failure to comply with such covenants could cause a default under the applicable debt agreement, and we may then be required to repay such debt with capital from other sources. Under those circumstances, other sources of capital may not be available to us, or be available only on unattractive terms. Additionally, in the future our ability to satisfy current or prospective lenders’ insurance requirements may be adversely affected if lenders generally insist upon greater insurance coverage against acts of terrorism or losses resulting from earthquakes than is available to us in the marketplace or on commercially reasonable terms.

We rely on debt financing, including borrowings under our unsecured credit facility, issuances of unsecured debt securities and debt secured by individual properties, to finance our existing portfolio, our acquisition and development activities and for working capital. If we are unable to obtain debt financing from these or other sources, or to refinance existing indebtedness upon maturity, our financial condition and results of operations would likely be adversely affected. If we breach covenants in our debt agreements, the lenders can declare a default and, if the debt is secured, can take possession of the property securing the defaulted loan. In addition, our unsecured debt agreements contain specific cross-default provisions with respect to specified other indebtedness, giving the unsecured lenders the right to declare a default if we are in default under other loans in some circumstances. Defaults under our debt agreements could materially and adversely affect our financial condition and results of operations.

Our degree of leverage could limit our ability to obtain additional financing or affect the market price of our common stock or debt securities.

On February 18, 2011,21, 2013, our total consolidated debt was approximately $8.0$8.9 billion (i.e., excluding unconsolidated joint venture debt). Consolidated debt to total consolidated market capitalization ratio, defined as total consolidated debt as a percentage of the market value of our outstanding equity securities plus our total consolidated debt, is a measure of leverage commonly used by analysts in the REIT sector. Our total consolidated market capitalization was approximately $23.6$26.9 billion at February 18, 2011.21, 2013. Total consolidated market capitalization was calculated using the closing stock price of $94.99$105.46 per common share and the following: (1) 141,864,497151,639,342 shares of our common stock, (2) 19,387,31116,050,062 outstanding common units of limited partnership interest in Boston Properties Limited Partnership (excluding common units held by Boston Properties, Inc.)us), (3) an aggregate of 1,460,6881,307,083 common units issuable upon conversion of all outstanding Series Two Preferred Units of partnership interest in Boston Properties Limited Partnership, (4) an aggregate of 1,682,0951,451,534 common units issuable upon conversion of all outstanding LTIP Units, assuming all conditions have been met for the conversion of the LTIP Units, (5) 1,221,527 Series Four Preferred Units of partnership interest multiplied by the fixed liquidation preference of $50 per unit and (5)(6) our consolidated debt totaling approximately $8.0$8.9 billion. The calculation of total consolidated market capitalization does not include 400,000 2011 OPP Units, 400,000 2012 OPP Units and 280,000 MYLTIP Units because, unlike other LTIP Units, they are not earned until certain return thresholds are achieved. Our total consolidated debt, which excludes debt collateralized by our unconsolidated joint ventures, at February 18, 201121, 2013 represented approximately 33.74%33.03% of our total consolidated market capitalization. This percentage will fluctuate with changes in the market price of our common stock and does not necessarily reflect our capacity to incur additional debt to finance our activities or our ability to manage our existing debt obligations. However, for a company like ours, whose assets are primarily income-producing real estate, the consolidated debt to total consolidated market capitalization ratio may provide investors with an alternate indication of leverage, so long as it is evaluated along with other financial ratios and the various components of our outstanding indebtedness.

Our degree of leverage could affect our ability to obtain additional financing for working capital, capital expenditures, acquisitions, development or other general corporate purposes. Our senior unsecured debt is currently rated investment grade by the three major rating agencies. However, there can be no assurance that we will be able to maintain this rating, and in the event our senior debt is downgraded from its current rating, we would likely incur higher borrowing costs and/or difficulty in obtaining additional financing. Our degree of leverage could also make us more vulnerable to a downturn in business or the economy generally. There is a risk that changes in our debt to market capitalization ratio, which is in part a function of our stock price, or our ratio of indebtedness to other measures of asset value used by financial analysts may have an adverse effect on the market price of our equity or debt securities.

We face risks associated with property acquisitions.

We have acquired in the past and intend to continue to pursue the acquisition of properties and portfolios of properties, including large portfolios that could increase our size and result in alterations to our capital structure. Our acquisition activities and their success are subject to the following risks:

We have acquired in the past and in the future may acquire properties through the acquisition of first mortgage or mezzanine debt. Investments in these loans must be carefully structured to ensure that we satisfy the various asset and income requirements applicable to REITs. If we fail to structure any such acquisition properly, we could fail to qualify as a REIT. In addition, acquisitions of first mortgage or mezzanine loans subject us to the risks associated with the borrower’s default, including potential bankruptcy, and there may be significant delays and costs associated with the process of foreclosure on collateral securing or supporting these investments. There can be no assurance that we would recover any or all of our investment in the event of such a default or bankruptcy.

We have acquired in the past and in the future may acquire properties or portfolios of properties through tax deferred contribution transactions in exchange for partnership interests in BPLP. This acquisition structure has the effect, among others, of reducing the amount of tax depreciation we can deduct over the tax life of the acquired properties, and typically requires that we agree to protect the contributors’ ability to defer recognition of taxable gain through restrictions on our ability to dispose of the acquired properties and/or the allocation of partnership debt to the contributors to maintain their tax bases. These restrictions could limit our ability to sell an asset at a time, or on terms, that would be favorable absent such restrictions.

Any future international activities will be subject to special risks and we may not be able to effectively manage our international business.

We have underwritten, and in the future may acquire, properties, portfolios of properties or interests in real-estate related entities on a strategic or selective basis in international markets that are new to us. If we acquire properties or platforms located in these markets, we will face risks associated with a lack of market knowledge and understanding of the local economy, forging new business relationships in the area and unfamiliarity with local laws and government and permitting procedures. In addition, our international operations will be subject to the usual risks of doing business abroad such as possible revisions in tax treaties or other laws and regulations,

including those governing the taxation of our international income, restrictions on the transfer of funds and uncertainty over terrorist activities. We cannot predict the likelihood that any of these developments may occur. Further, we may in the future enter into agreements with non-U.S. entities that are governed by the laws of, and are subject to dispute resolution in the courts of, another country or region. We cannot accurately predict whether such a forum would provide us with an effective and efficient means of resolving disputes that may arise.

Investments in international markets may also subject us to risks associated with funding increasing headcount, integrating new offices, and establishing effective controls and procedures to regulate the operations of new offices and to monitor compliance with U.S. laws and regulations such as the Foreign Corrupt Practices Act and similar foreign laws and regulations.

We may be subject to risks from potential fluctuations in exchange rates between the U.S. dollar and the currencies of the other countries in which we invest.

If we invest in countries where the U.S. dollar is not the national currency, we will be subject to international currency risks from the potential fluctuations in exchange rates between the U.S. dollar and the currencies of those other countries. A significant depreciation in the value of the currency of one or more countries where we have a significant investment may materially affect our results of operations. We may attempt to mitigate any such effects by borrowing in the currency of the country in which we are investing and, under certain circumstances, by hedging exchange rate fluctuations; however, access to capital may be more restricted, or unavailable on favorable terms or at all, in certain locations. For leases denominated in international currencies, we may use derivative financial instruments to manage the international currency exchange risk. We cannot assure you, however, that our efforts will successfully neutralize all international currency risks.

Acquired properties may expose us to unknown liability.

We may acquire properties subject to liabilities and without any recourse, or with only limited recourse, against the prior owners or other third parties with respect to unknown liabilities. As a result, if a liability were asserted against us based upon ownership of those properties, we might have to pay substantial sums to settle or contest it, which could adversely affect our results of operations and cash flow. Unknown liabilities with respect to acquired properties might include:

Competition for acquisitions may result in increased prices for properties.

We plan to continue to acquire properties as we are presented with attractive opportunities. We may face competition for acquisition opportunities with other investors, and this competition may adversely affect us by subjecting us to the following risks:

Our use of joint ventures may limit our flexibility with jointly owned investments.

In appropriate circumstances, we intend to develop and acquire properties in joint ventures with other persons or entities when circumstances warrant the use of these structures. We currently have twelvethirteen joint ventures that are not consolidated with our financial statements. Our share of the aggregate revenue of these joint ventures represented approximately 17.9%14.3% of our total revenue (the sum of our total consolidated revenue and our share of such joint venture revenue) for the year ended December 31, 2010.2012. Our participation in joint ventures is subject to the risks that:

Our properties face significant competition.

We face significant competition from developers, owners and operators of office and residential properties and other commercial real estate, including sublease space available from our tenants. Substantially all of our properties face competition from similar properties in the same market. This competition may affect our ability to attract and retain tenants and may reduce the rents we are able to charge. These competing properties may have vacancy rates higher than our properties, which may result in their owners being willing to lease available space at lower rates than the space in our properties.

We face potential difficulties or delays renewing leases or re-leasing space.

We derive most of our income from rent received from our tenants. If a tenant experiences a downturn in its business or other types of financial distress, it may be unable to make timely rental payments. Also, when our tenants decide not to renew their leases or terminate early, we may not be able to re-let the space. Even if tenants decide to renew or lease new space, the terms of renewals or new leases, including the cost of required renovations or concessions to tenants, may be less favorable to us than current lease terms. As a result, our cash flow could decrease and our ability to make distributions to our securityholders could be adversely affected.

We face potential adverse effects from major tenants’ bankruptcies or insolvencies.

The bankruptcy or insolvency of a major tenant may adversely affect the income produced by our properties. Our tenants could file for bankruptcy protection or become insolvent in the future. We cannot evict a tenant solely because of its bankruptcy. On the other hand, a bankrupt tenant may reject and terminate its lease with us. In such case, our claim against the bankrupt tenant for unpaid and future rent would be subject to a statutory cap that might be substantially less than the remaining rent actually owed under the lease, and, even so, our claim for unpaid rent would likely not be paid in full. This shortfall could adversely affect our cash flow and results of operations.

We may have difficulty selling our properties, which may limit our flexibility.

Large and high-quality office and hotel propertiesProperties like the ones that we own could be difficult to sell. This may limit our ability to change our portfolio promptly in response to changes in economic or other conditions. In addition, federal tax laws limit our ability to sell properties and this may affect our ability to sell properties without adversely affecting returns to our securityholders. These restrictions reduce our ability to respond to changes in the performance of our investments and could adversely affect our financial condition and results of operations.

Our ability to dispose of some of our properties is constrained by their tax attributes. Properties which we developed and have owned for a significant period of time or which we acquired through tax deferred contribution transactions in exchange for partnership interests in BPLP often have low tax bases. Furthermore, as a REIT, we may be subject to a 100% “prohibited transactions” tax on the gain from dispositions of property if we are deemed to hold the property primarily for sale to customers in the ordinary course of business, unless the disposition qualifies under a safe harbor exception for properties that have been held for at least two years and with respect to which certain other requirements are met. The potential application of the prohibited transactions tax could cause us to forego potential dispositions of property or other opportunities that might otherwise be attractive to us, or to undertake such dispositions or other opportunities through a taxable REIT subsidiary, which would generally result in income taxes being incurred. If we dispose of these properties outright in taxable transactions, we may be required to distribute a significant amount of the taxable gain to our securityholders under the requirements of the Internal Revenue Code for REITs, which in turn would impact our cash flow and increase our leverage. In some cases, without incurring additional costs we may be restricted from disposing of properties contributed in exchange for our partnership interests under tax protection agreements with contributors. To dispose of low basis or tax-protected properties efficiently we from time to time use like-kind exchanges, which qualify for non-recognition of taxable gain, but can be difficult to consummate and result in the property for which the disposed assets are exchanged inheriting their low tax bases and other tax attributes (including tax protection covenants).

Because we own a hotel property, we face the risks associated with the hospitality industry.

Because the lease payments we receive under our hotel lease are based on a participation in the gross receipts of the hotel, if the hotel does not generate sufficient receipts, our cash flow would be decreased, which could reduce the amount of cash available for distribution to our securityholders. The following factors, among others, are common to the hotel industry, and may reduce the receipts generated by our hotel property:

In addition, because our hotel property is located in Cambridge, Massachusetts, it is subject to the Cambridge market’s fluctuations in demand, increases in operating costs and increased competition from additions in supply.

We face risks associated with short-term liquid investments.

We continue to have significant cash balances that we invest in a variety of short-term investments that are intended to preserve principal value and maintain a high degree of liquidity while providing current income. From time to time, these investments may include (either directly or indirectly):

Investments in these securities and funds are not insured against loss of principal. Under certain circumstances we may be required to redeem all or part of our investment, and our right to redeem some or all of our investment may be delayed or suspended. In addition, there is no guarantee that our investments in these securities or funds will be redeemable at par value. A decline in the value of our investment or a delay or suspension of our right to redeem may have a material adverse effect on our results of operations or financial condition.

Failure to qualify as a real estate investment trust would cause us to be taxed as a corporation, which would substantially reduce funds available for payment of dividends.

If we fail to qualify as a real estate investment trust, or REIT for federal income tax purposes, we will be taxed as a corporation unless certain relief provisions apply. We believe that we are organized and qualified as a REIT and intend to operate in a manner that will allow us to continue to qualify as a REIT. However, we cannot assure you that we are qualified as such, or that we will remain qualified as such in the future. This is because qualification as a REIT involves the application of highly technical and complex provisions of the Internal Revenue Code as to which there are only limited judicial and administrative interpretations and involves the determination of facts and circumstances not entirely within our control. Future legislation, new regulations, administrative interpretations or court decisions may significantly change the tax laws or the application of the tax laws with respect to qualification as a REIT for federal income tax purposes or the federal income tax consequences of such qualification.

In addition, we currently hold certain of our properties and the Value-Added Fund holds its properties, through a subsidiarysubsidiaries that hashave elected to be taxed as a REITREITs and we may in the future determine that it is in our best interests to hold one or more of our other properties through one or more subsidiaries that elect to be taxed as REITs. If any of these subsidiaries fails to qualify as a REIT for federal income tax purposes, then we may also fail to qualify as a REIT for federal income tax purposes.

If we fail to qualify as a REIT then, unless certain relief provisions apply, we will face serious tax consequences that will substantially reduce the funds available for payment of dividends for each of the years involved because:

In addition, if we fail to qualify as a REIT and the relief provisions do not apply, we will no longer be required to pay dividends. As a result of all these factors, our failure to qualify as a REIT could impair our ability to expand our business and raise capital, and it would adversely affect the value of our common stock. If we fail to qualify as a REIT but are eligible for certain relief provisions, then we may retain our status as a REIT but may be required to pay a penalty tax, which could be substantial.

In order to maintain our REIT status, we may be forced to borrow funds during unfavorable market conditions or to pay taxable dividends of our common stock.conditions.

In order to maintain our REIT status, we may need to borrow funds on a short-term basis to meet the REIT distribution requirements, even if the then-prevailing market conditions are not favorable for these borrowings or, alternatively, for 2011, we could pay a taxable stock dividend.borrowings. To qualify as REIT, we generally must distribute to our stockholders at least 90% of our net taxable income each year, excluding capital gains. In addition, we will be subject to a 4% nondeductible excise tax on the amount, if any, by which dividends paid by us in any calendar year are less than the sum of 85% of our ordinary income, 95% of our capital gain net income and 100% of our undistributed income from prior years. We may need short-term debt or long-term debt or proceeds from asset sales, creation of joint ventures or sales of common stock to fund required distributions as a result of differences in timing between the actual receipt of income and the recognition of income for federal income tax purposes, or the effect of non-deductible capital expenditures, the creation of reserves or required debt or amortization payments. The inability of our cash flows to cover our distribution requirements could have an adverse impact on our ability to raise short—short - and long-term debt or sell equity securities in order to fund distributions required to maintain our REIT status. Alternatively, under recent IRS guidance that is effective through 2011, we may elect to distribute taxable dividends that are payable up to 90% in the form of our common stock (with the remainder payable in cash). In this event, shareholders will be required to include the full amount of the dividend in income, and shareholder’s tax liability could exceed the cash portion of their dividend.

Limits on changes in control may discourage takeover attempts beneficial to stockholders.

Provisions in our certificate of incorporationCharter and bylaws, our shareholder rights agreement and the limited partnership agreement of BPLP, as well as provisions of the Internal Revenue Code and Delaware corporate law, may:

Stock Ownership Limit

To facilitate maintenance of our qualification as a REIT and to otherwise address concerns relating to concentration of capital stock ownership, our certificate of incorporationCharter generally prohibits ownership, directly, indirectly or beneficially, by any single stockholder of more than 6.6% of the number of outstanding shares of any class or series of our common stock. We refer to this limitation as the “ownership limit.” Our Board of Directors may waive, in its sole discretion, or modify the ownership limit with respect to one or more persons if it is satisfied that ownership in excess of this limit will not jeopardize our status as a REIT for federal income tax purposes. In addition, under our certificate of incorporationCharter each of Mortimer B. Zuckerman and the respective families and affiliates of Mortimer B. Zuckerman and Edward H. Linde, as well as, in general, pension plans and mutual funds, may actually and beneficially own up to 15% of the number of outstanding shares of any class or series of our equity common stock. Shares owned in violation of the ownership limit will be subject to the loss of rights to distributions and voting and other penalties. The ownership limit may have the effect of inhibiting or impeding a change in control.

BPLP’s Partnership Agreement

We have agreed in the limited partnership agreement of BPLP not to engage in specified extraordinary transactions, including, among others, business combinations, unless limited partners of BPLP other than Boston Properties, Inc.us receive, or have the opportunity to receive, either (1) the same consideration for their partnership interests as

holders of our common stock in the transaction or (2) limited partnership units that, among other things, would entitle the holders, upon redemption of these units, to receive shares of common equity of a publicly traded company or the same consideration as holders of our common stock received in the transaction. If these limited partners would not receive such consideration, we cannot engage in the transaction unless limited partners holding at least 75% of the common units of limited partnership interest, other than those held by Boston Properties, Inc. or its affiliates, consent to the transaction. In addition, we have agreed in the limited partnership agreement of BPLP that we will not complete specified extraordinary transactions, including among others, business combinations, in which we receive the approval of our common stockholders unless (1) limited partners holding at least 75% of the common units of limited partnership interest, other than those held by Boston Properties, Inc. or its affiliates, consent to the transaction or (2) the limited partners of BPLP are also allowed to vote and the transaction would have been approved had these limited partners been able to vote as common stockholders on the transaction. Therefore, if our common stockholders approve a specified extraordinary transaction, the partnership agreement requires the following before we can complete the transaction:

As a result of these provisions, a potential acquirer may be deterred from making an acquisition proposal, and we may be prohibited by contract from engaging in a proposed extraordinary transaction, including a proposed business combination, even though our stockholders approve of the transaction.

Shareholder Rights Plan

We have a shareholder rights plan. Under the terms of this plan, we can in effect prevent a person or group from acquiring more than 15% of the outstanding shares of our common stock because, unless we approve of the acquisition, after the person acquires more than 15% of our outstanding common stock, all other stockholders will have the right to purchase securities from us at a price that is less than their then fair market value. This would substantially reduce the value and influence of the stock owned by the acquiring person. Our Board of Directors can prevent the plan from operating by approving the transaction in advance, which gives us significant power to approve or disapprove of the efforts of a person or group to acquire a large interest in our company.

Changes in market conditions could adversely affect the market price of our common stock.

As with other publicly traded equity securities, the value of our common stock depends on various market conditions that may change from time to time. Among the market conditions that may affect the value of our common stock are the following:

The market value of our common stock is based primarily upon the market’s perception of our growth potential and our current and potential future earnings and cash dividends. Consequently, our common stock may trade at prices that are greater or less than our net asset value per share of common stock. If our future earnings or cash dividends are less than expected, it is likely that the market price of our common stock will diminish.

Further issuances of equity securities may be dilutive to current securityholders.

The interests of our existing securityholders could be diluted if additional equity securities are issued to finance future developments, acquisitions, or repay indebtedness. Our ability to execute our business strategy depends on our access to an appropriate blend of debt financing, including unsecured lines of credit and other forms of secured and unsecured debt, and equity financing, including common and preferred equity.

The number of shares available for future sale could adversely affect the market price of our stock.

In connection with and subsequent to our initial public offering, we have completed many private placement transactions in which shares of capital stock of Boston Properties, Inc. or partnership interests in BPLP were issued to owners of properties we acquired or to institutional investors. This common stock, or common stock issuable in exchange for such partnership interests in BPLP, may be sold in the public securities markets over time under registration rights we granted to these investors. Additional common stock issuable under our employee benefit and other incentive plans, including as a result of the grant of stock options and restricted equity securities, may also be sold in the market at some time in the future. Future sales of our common stock in the market could adversely affect the price of our common stock. We cannot predict the effect the perception in the market that such sales may occur will have on the market price of our common stock.

We may change our policies without obtaining the approval of our stockholders.

Our operating and financial policies, including our policies with respect to acquisitions of real estate, growth, operations, indebtedness, capitalization and dividends, are exclusively determined by our Board of Directors. Accordingly, our securityholders do not control these policies.

Our success depends on key personnel whose continued service is not guaranteed.

We depend on the efforts of key personnel, particularly Mortimer B. Zuckerman, Chairman of our Board and Chief Executive Officer, and Douglas T. Linde, our President.President, and Raymond A. Ritchey, Executive Vice President, National Director of Acquisition and Development. Among the reasons that Messrs. Zuckerman, and D. Linde and Ritchey are important to our success is that each has a national reputation, which attracts business and investment opportunities and assists us in negotiations with lenders, joint venture partners and other investors. If we lost their services, our relationships with lenders, potential tenants and industry personnel could diminish. Mr. Zuckerman has substantial outside business interests that could interfere with his ability to devote his full time to our business and affairs.

Our two Executive Vice Presidents, our Chief Financial Officer and five Regional Managers also have strong reputations. Their reputations aid us in identifying opportunities, having opportunities brought to us, and negotiating with tenants and build-to-suit prospects. While we believe that we could find replacements for these key personnel, the loss of their services could materially and adversely affect our operations because of diminished relationships with lenders, prospective tenants and industry personnel.

Conflicts of interest exist with holders of interests in BPLP.

Sales of properties and repayment of related indebtedness will have different effects on holders of interests in BPLP than on our stockholders.

Some holders of interests in BPLP, including Mr. Zuckerman, and the estate of Mr. E. Linde, could incur adverse tax consequences upon the sale of certain of our properties and on the repayment of related debt which differ from the tax consequences to us and our stockholders. Consequently, these holders of partnership interests in BPLP may have different objectives regarding the appropriate pricing and timing of any such sale or repayment of debt. While we have exclusive authority under the limited partnership agreement of BPLP to determine when to refinance or repay debt or whether, when, and on what terms to sell a property, subject, in the case of certain properties, to the contractual commitments described below, any such decision would require the approval of our Board of Directors. While the Board of Directors has a policy with respect to these matters, as directors and executive officers, Messrs. Zuckerman and D. Linde could exercise their influence in a manner inconsistent with the interests of some, or a majority, of our stockholders, including in a manner which could prevent completion of a sale of a property or the repayment of indebtedness.

Agreement not to sell some properties.

We have entered into agreements with respect to some properties that we have acquired in exchange for partnership interests in BPLP. Pursuant to those agreements, we have agreed not to sell or otherwise transfer some of our properties, prior to specified dates, in any transaction that would trigger taxable income and we are responsible for the reimbursement of certain tax-related costs to the prior owners if the subject properties are sold in a taxable sale. In general, our obligations to the prior owners are limited in time and only apply to actual damages suffered. As of December 31, 20102012 there were a total of sixseven properties subject to these restrictions. In the aggregate, all properties subject to the restrictions accounted for approximately 24%17% of our total revenue (the sum of our total consolidated revenue and our share of joint venture revenue) for the year ended December 31, 2010.2012.

BPLP has also entered into agreements providing prior owners of properties with the right to guarantee specific amounts of indebtedness and, in the event that the specific indebtedness they guarantee is repaid or reduced, additional and/or substitute indebtedness. These agreements may hinder actions that we may otherwise desire to take to repay or refinance guaranteed indebtedness because we would be required to make payments to the beneficiaries of such agreements if we violate these agreements.

Mr. Zuckerman will continue to engage in other activities.

Mr. Zuckerman has a broad and varied range of investment interests. He could acquire an interest in a company which is not currently involved in real estate investment activities but which may acquire real property in the future. However, pursuant to his employment agreement, Mr. Zuckerman will not, in general, have management control over such companies and, therefore, he may not be able to prevent one or more of such companies from engaging in activities that are in competition with our activities.

Compliance or failure to comply with the Americans with Disabilities Act or other safety regulations and requirements could result in substantial costs.

The Americans with Disabilities Act generally requires that public buildings, including office buildings and hotels, be made accessible to disabled persons. Noncompliance could result in the imposition of fines by the federal government or the award of damages to private litigants. If, under the Americans with Disabilities Act, we are required to make substantial alterations and capital expenditures in one or more of our properties, including the removal of access barriers, it could adversely affect our financial condition and results of operations, as well as the amount of cash available for distribution to our securityholders.

Our properties are subject to various federal, state and local regulatory requirements, such as state and local fire and life safety requirements. If we fail to comply with these requirements, we could incur fines or private damage awards. We do not know whether existing requirements will change or whether compliance with future requirements will require significant unanticipated expenditures that will affect our cash flow and results of operations.

Failure to comply with Federal government contractor requirements could result in substantial costs and loss of substantial revenue.

We are subject to compliance with a wide variety of complex legal requirements because we are a Federal government contractor. These laws regulate how we conduct business, require us to administer various compliance programs and require us to impose compliance responsibilities on some of our contractors. Our failure to comply with these laws could subject us to fines and penalties, cause us to be in default of our leases and other contracts with the Federal government and bar us from entering into future leases and other contracts with the Federal government. There can be no assurance that these costs and loss of revenue will not have a material adverse effect on our properties, operations or business.

Some potential losses are not covered by insurance.

We carry insurance coverage on our properties of types and in amounts and with deductibles that we believe are in line with coverage customarily obtained by owners of similar properties. In response to the uncertainty in the insurance market following the terrorist attacks of September 11, 2001, the Federal Terrorism Risk Insurance Act (as amended, “TRIA”) was enacted in November 2002 to require regulated insurers to make available coverage for “certified” acts of terrorism (as defined by the statute). The expiration date of TRIA was extended to December 31, 2014 by the Terrorism Risk Insurance Program Reauthorization Act of 2007 (“TRIPRA”). and we can provide no assurance that it will be extended further. Currently, the per occurrence limits of our portfolio property insurance program are $1.0 billion, including coverage for acts of terrorism certified under TRIA other than nuclear, biological, chemical or radiological terrorism (“Terrorism Coverage”). We currently insure certainalso carry $250 million of Terrorism Coverage for 601 Lexington Avenue, New York, New York (“601 Lexington Avenue”) in excess of the $1.0 billion of Terrorism Coverage in our property insurance program which is provided by IXP, LLC (“IXP”) as a direct insurer. Certain properties, including the General Motors Building located at 767 Fifth Avenue in New York, New York (“767 Fifth Avenue”), are currently insured in a separate stand alone insurance program.programs. The property insurance program per occurrence limits for 767 Fifth Avenue are $1.625 billion, including Terrorism Coverage, with $1.375 billion of Terrorism Coverage in excess of $250 million being provided by NYXP, LLC, (“NYXP”) as a direct insurer. We also currently carry nuclear, biological, chemical and radiological terrorism insurance coverage for acts of terrorism certified under TRIA (“NBCR Coverage”), which is provided by IXP, LLC (“IXP”) as a direct insurer, for the properties in our portfolio, including 767 Fifth Avenue, but excluding the properties owned by our Value-Added Fund and certain other properties owned in joint ventures with third parties or which we manage. The per occurrence limit for NBCR Coverage is $1 billion. Under TRIA, after the payment of the required deductible and coinsurance, the additional Terrorism Coverage provided by IXP for 601 Lexington Avenue, the NBCR Coverage provided by IXP and the Terrorism Coverage provided by NYXP are backstopped by the Federal Government if the aggregate industry insured losses resulting from a certified act of terrorism exceed a “program trigger.” The program trigger is $100 million and the coinsurance is 15%. Under TRIPRA, if the Federal Government pays out for a loss under TRIA, it is mandatory that the Federal Government recoup the full amount of the loss from insurers offering TRIA coverage after the payment of the loss pursuant to a formula in TRIPRA. We may elect to terminate the NBCR Coverage if the Federal Government seeks recoupment for losses paid under TRIA, if there is a change in our portfolio or for any other reason. In the event TRIPRA is not extended beyond December 31, 2014, (i) we may pursue alternative approaches to secure coverage for acts of terrorism thereby potentially increasing our overall cost of insurance, (ii) if such insurance is not available at commercially reasonable rates with limits equal to our current coverage or at all, we may not continue to have full occurrence limit coverage for acts of terrorism, (iii) we may not satisfy the insurance requirements under existing or future debt financings secured by individual properties and (iv) we

may not be able to obtain future debt financings secured by individual properties. We intend to continue to monitor the scope, nature and cost of available terrorism insurance and maintain terrorism insurance in amounts and on terms that are commercially reasonable.

We also currently carry earthquake insurance on our properties located in areas known to be subject to earthquakes in an amount and subject to self-insurance that we believe are commercially reasonable. In addition, this insurance is subject to a deductible in the amount of 5% of the value of the affected property. Specifically, we currently carry earthquake insurance which covers our San Francisco region (excluding 680 Folsom Street) with a $120 million per occurrence limit and a $120 million annual aggregate limit, $20 million of which is provided by IXP, as a direct

insurer. In addition, the builders risk policy maintained for the development of 680 Folsom Street in San Francisco includes a $20 million per occurrence and annual aggregate limit of earthquake coverage. The amount of our earthquake insurance coverage may not be sufficient to cover losses from earthquakes. In addition, the amount of earthquake coverage could impact our ability to finance properties subject to earthquake risk. We may discontinue earthquake insurance on some or all of our properties in the future if the premiums exceed our estimation of the value of the coverage.

IXP, a captive insurance company which is a wholly-owned subsidiary, acts as a direct insurer with respect to a portion of our earthquake insurance coverage for our Greater San Francisco properties, the additional Terrorism Coverage for 601 Lexington Avenue and our NBCR Coverage. The additional Terrorism Coverage provided by IXP for 601 Lexington Avenue only applies to losses which exceed the program trigger under TRIA. NYXP, a captive insurance company which is a wholly-owned subsidiary, acts as a direct insurer with respect to a portion of our Terrorism Coverage for 767 Fifth Avenue. Currently, NYXP only insures losses which exceed the program trigger under TRIA and NYXP reinsures with a third-party insurance company any coinsurance payable under TRIA. Insofar as we own IXP and NYXP, we are responsible for their liquidity and capital resources, and the accounts of IXP and NYXP are part of our consolidated financial statements. In particular, if a loss occurs which is covered by our NBCR Coverage but is less than the applicable program trigger under TRIA, IXP would be responsible for the full amount of the loss without any backstop by the Federal Government. IXP and NYXP would also be responsible for any recoupment charges by the Federal Government in the event losses are paid out and their insurance policies are maintained after the payout by the Federal Government. If we experience a loss and IXP or NYXP are required to pay under their insurance policies, we would ultimately record the loss to the extent of the required payment. Therefore, insurance coverage provided by IXP and NYXP should not be considered as the equivalent of third-party insurance, but rather as a modified form of self-insurance. In addition, our Operating Partnership has issued a guarantee to cover liabilities of IXP in the amount of $20.0 million.

The mortgages on our properties typically contain requirements concerning the financial ratings of the insurers who provide policies covering the property. We provide the lenders on a regular basis with the identity of the insurance companies in our insurance programs. The ratings of some of our insurers are below the rating requirements in some of our loan agreements and the lenders for these loans could attempt to claim an event of default has occurred under the loan. We believe we could obtain insurance with insurers which satisfy the rating requirements. Additionally, in the future our ability to obtain debt financing secured by individual properties, or the terms of such financing, may be adversely affected if lenders generally insist on ratings for insurers or amounts of insurance which are difficult to obtain or which result in a commercially unreasonable premium. There can be no assurance that a deficiency in the financial ratings of one or more of our insurers will not have a material adverse effect on us.

We continue to monitor the state of the insurance market in general, and the scope and costs of coverage for acts of terrorism and California earthquake risk in particular, but we cannot anticipate what coverage will be available on commercially reasonable terms in future policy years. There are other types of losses, such as from wars, or the presence of mold at our properties, for which we cannot obtain insurance at all or at a reasonable cost. With respect to such losses and losses from acts of terrorism, earthquakes or other catastrophic events, if we experience a loss that is uninsured or that exceeds policy limits, we could lose the capital invested in the damaged properties, as well as the anticipated

future revenues from those properties. Depending on the specific circumstances of each affected property, it is possible that we could be liable for mortgage indebtedness or other obligations related to the property. Any such loss could materially and adversely affect our business and financial condition and results of operations.

Actual or threatened terrorist attacks may adversely affect our ability to generate revenues and the value of our properties.

We have significant investments in large metropolitan markets that have been or may be in the future the targets of actual or threatened terrorism attacks, including midtown Manhattan,Boston, New York, San Francisco and Washington, DC, Boston and San Francisco.DC. As a result, some tenants in these markets may choose to relocate their businesses to other markets or to lower-profile office buildings within these markets that may be perceived to be less likely targets of future terrorist activity. This could result in an overall decrease in the demand for office space in these markets generally or in our properties in particular, which could increase vacancies in our properties or necessitate that we lease our properties on less favorable terms or both. In addition, future terrorist attacks in these markets could

directly or indirectly damage our properties, both physically and financially, or cause losses that materially exceed our insurance coverage. As a result of the foregoing, our ability to generate revenues and the value of our properties could decline materially. See also “—Some potential losses are not covered by insurance.”

We face risks associated with our tenants being designated “Prohibited Persons” by the Office of Foreign Assets Control.

Pursuant to Executive Order 13224 and other laws, the Office of Foreign Assets Control of the United States Department of the Treasury (“OFAC”) maintains a list of persons designated as terrorists or who are otherwise blocked or banned (“Prohibited Persons”). OFAC regulations and other laws prohibit conducting business or engaging in transactions with Prohibited Persons (the “OFAC Requirements”). Certain of our loan and other agreements require us to comply with OFAC Requirements. We have established a compliance program whereby tenants and others with whom we conduct business are checked against the OFAC list of Prohibited Persons prior to entering into any agreement and on a periodic basis thereafter. Our leases and other agreements, in general, require the other party to comply with OFAC Requirements. If a tenant or other party with whom we contract is placed on the OFAC list we may be required by the OFAC Requirements to terminate the lease or other agreement. Any such termination could result in a loss of revenue or a damage claim by the other party that the termination was wrongful.

We face possible risks associated with the physical effects of climate change.

We cannot predictassert with certainty whether climate change is occurring and, if so, at what rate. However, the physical effects of climate change could have a material adverse effect on our properties, operations and business. For example, many of our properties are located along the East and West coasts, particularly those in the Central Business Districts of midtown Manhattan, Boston, New York, and San Francisco. To the extent climate change causes changes in weather patterns, our markets could experience increases in storm intensity and rising sea-levels. Over time, these conditions could result in declining demand for office space in our buildings or theour inability of us to operate the buildings at all. Climate change may also have indirect effects on our business by increasing the cost of (or making unavailable) property insurance on terms we find acceptable, increasing the cost of energy and increasing the cost of snow removal at our properties. There can be no assurance that climate change will not have a material adverse effect on our properties, operations or business.

Potential liability for environmental contamination could result in substantial costs.

Under federal, state and local environmental laws, ordinances and regulations, we may be required to investigate and clean up the effects of releases of hazardous or toxic substances or petroleum products at our properties simply because of our current or past ownership or operation of the real estate. If unidentified environmental problems arise, we may have to make substantial payments, which could adversely affect our cash

flow and our ability to make distributions to our securityholders, because:

These costs could be substantial and in extreme cases could exceed the amount of our insurance or the value of the contaminated property. We currently carry environmental insurance in an amount and subject to deductibles that we believe are commercially reasonable. Specifically, we carry a pollution legal liability policy with a $10 million limit per incident and a policy aggregate limit of $30 million. The presence of hazardous or toxic substances or petroleum products or the failure to properly remediate contamination may materially and adversely affect our ability to borrow against, sell or rent an affected property. In addition, applicable environmental laws create liens on contaminated sites in favor of the government for damages and costs it incurs in connection with a contamination. Changes in laws, regulations and practices and their implementation increasing the potential liability for environmental conditions existing at our properties, or increasing the restrictions on the handling, storage or discharge of hazardous or toxic substances or petroleum products or other actions may result in significant unanticipated expenditures.

Environmental laws also govern the presence, maintenance and removal of asbestos. Suchasbestos and other building materials. For example, laws require that owners or operators of buildings containing asbestos:

Such laws may impose fines and penalties on building owners or operators who fail to comply with these requirements and may allow third parties to seek recovery from owners or operators for personal injury associated with exposure to asbestos fibers.

Some of our properties are located in urban and previously developed areas where fill or current or historic industrial uses of the areas have caused site contamination. It is our policy to retain independent environmental consultants to conduct or update Phase I environmental site assessments and asbestos surveys with respect to our acquisition of properties. These assessments generally include a visual inspection of the properties and the surrounding areas, an examination of current and historical uses of the properties and the surrounding areas and a review of relevant state, federal and historical documents, but do not involve invasive techniques such as soil and ground water sampling. Where appropriate, on a property-by-property basis, our practice is to have these consultants conduct additional testing, including sampling for asbestos, for lead in drinking water and, for soil and/or groundwater contamination where underground storage tanks are or were located or where other past site usage creates a potential environmental problem. Even though these environmental assessments are conducted, there is still the risk that:

Inquiries about indoor air quality may necessitate special investigation and, depending on the results, remediation beyond our regular indoor air quality testing and maintenance programs. Indoor air quality issues can stem from inadequate ventilation, chemical contaminants from indoor or outdoor sources, and biological contaminants such as molds, pollen, viruses and bacteria. Indoor exposure to chemical or biological contaminants above certain levels can be alleged to be connected to allergic reactions or other health effects and symptoms in susceptible individuals. If these conditions were to occur at one of our properties, we may be subject to third-party claims for personal injury, or may need to undertake a targeted remediation program, including without limitation, steps to increase indoor ventilation rates and

eliminate sources of contaminants. Such remediation programs could be costly, necessitate the temporary relocation of some or all of the property’s tenants or require rehabilitation of the affected property.

We face risks associated with security breaches through cyber attacks, cyber intrusions or otherwise, as well as other significant disruptions of our information technology (IT) networks and related systems.

We face risks associated with security breaches, whether through cyber attacks or cyber intrusions over the Internet, malware, computer viruses, attachments to e-mails, persons inside our organization or persons with access to systems inside our organization, and other significant disruptions of our IT networks and related systems. The risk of a security breach or disruption, particularly through cyber attack or cyber intrusion, including by computer hackers, foreign governments and cyber terrorists, has generally increased as the number, intensity and sophistication of attempted attacks and intrusions from around the world have increased. Our IT networks and related systems are essential to the operation of our business and our ability to perform day-to-day operations (including managing our building systems) and, in some cases, may be critical to the operations of certain of our tenants. Although we make efforts to maintain the security and integrity of these types of IT networks and related systems, and we have implemented various measures to manage the risk of a security breach or disruption, there can be no assurance that our security efforts and measures will be effective or that attempted security breaches or disruptions would not be successful or damaging. Even the most well protected information, networks, systems and facilities remain potentially vulnerable because the techniques used in such attempted security breaches evolve and generally are not recognized until launched against a target, and in some cases are designed not be detected and, in fact, may not be detected. Accordingly, we may be unable to anticipate these techniques or to implement adequate security barriers or other preventative measures, and thus it is impossible for us to entirely mitigate this risk.

A security breach or other significant disruption involving our IT networks and related systems could:

Any or all of the foregoing could have a material adverse effect on our results of operations, financial condition and cash flows.

We did not obtain new owner’s title insurance policies in connection with properties acquired during our initial public offering.

We acquired many of our properties from our predecessors at the completion of our initial public offering in June 1997. Before we acquired these properties, each of them was insured by a title insurance policy. We did not obtain new owner’s title insurance policies in connection with the acquisition of these properties. To the extent we have financed properties after acquiring them in connection with the initial public offering, we have obtained new title insurance policies, however, the amount of these policies may be less than the current or future value of the applicable properties. Nevertheless, because in many instances we acquired these properties indirectly by acquiring ownership of the entity that owned the property and those owners remain in existence as our subsidiaries, some of these title insurance policies may continue to benefit us. Many of these title insurance policies may be for amounts less than the current or future values of the applicable properties. If there was a title defect related to any of these properties, or to any of the properties acquired at the time of our initial public offering, that is no longer covered by a title insurance policy, we could lose both our capital invested in and our anticipated profits from such property. We have obtained title insurance policies for all properties that we have acquired after our initial public offering, however, these policies may be for amounts less than the current or future values of the applicable properties.

Because of the ownership structure of our hotel property, we face potential adverse effects from changes to the applicable tax laws.

We own one hotel property. However, under the Internal Revenue Code, REITs like us are not allowed to operate hotels directly or indirectly. Accordingly, we lease our hotel property to one of our taxable REIT subsidiaries. As lessor, we are entitled to a percentage of the gross receipts from the operation of the hotel property. Marriott International, Inc. manages the hotel under the Marriott name pursuant to a management contract with the taxable REIT subsidiary as lessee. While the taxable REIT subsidiary structure allows the economic benefits of ownership to flow to us, the taxable REIT subsidiary is subject to tax on its income from the operations of the hotel at the federal and state level. In addition, the taxable REIT subsidiary is subject to detailed tax regulations that affect how it may be capitalized and operated. If the tax laws applicable to taxable REIT subsidiaries are modified, we may be forced to modify the structure for owning our hotel property, and such changes may adversely affect the cash flows from our hotel. In addition, the Internal Revenue Service, the United States Treasury Department and Congress frequently review federal income tax legislation, and we cannot predict whether, when or to what extent new federal tax laws, regulations, interpretations or rulings will be adopted. Any of such actions may prospectively or retroactively modify the tax treatment of the taxable REIT subsidiary and, therefore, may adversely affect our after-tax returns from our hotel property.

We face possible adverse changes in tax laws.

From time to time changes in state and local tax laws or regulations are enacted, which may result in an increase in our tax liability. A shortfall in tax revenues for states and municipalities in which we operate may lead to an increase in the frequency and size of such changes. If such changes occur, we may be required to pay additional taxes on our assets or income. These increased tax costs could adversely affect our financial condition and results of operations and the amount of cash available for the payment of dividends.

We face possible state and local tax audits.

Because we are organized and qualify as a REIT, we are generally not subject to federal income taxes, but areis subject to certain state and local taxes. In the normal course of business, certain entities through which we own real estate either have undergone, or are currently undergoing, tax audits. Although we believe that we have

substantial arguments in favor of our positions in the ongoing audits, in some instances there is no controlling precedent or interpretive guidance on the specific point at issue. Collectively, tax deficiency notices received to date from the jurisdictions conducting the ongoing audits have not been material. However, there can be no assurance that future audits will not occur with increased frequency or that the ultimate result of such audits will not have a material adverse effect on our results of operations.

Changes in accounting pronouncements could adversely affect our operating results, in addition to the reported financial performance of our tenants.

Accounting policies and methods are fundamental to how we record and report our financial condition and results of operations. Uncertainties posed by various initiatives of accounting standard-setting by the Financial Accounting Standards Board and the Securities and Exchange Commission, which create and interpret applicable accounting standards for U.S. companies, may change the financial accounting and reporting standards or their interpretation and application of these standards that govern the preparation of our financial statements. Proposed changes include, but are not limited to, changes in lease accounting and the adoption of accounting standards likely to require the increased use of “fair-value” measures.

These changes could have a material impact on our reported financial condition and results of operations. In some cases, we could be required to apply a new or revised standard retroactively, resulting in potentially material restatements of prior period financial statements. Similarly, these changes could have a material impact on our tenants’ reported financial condition or results of operations or could affect our tenants’ preferences regarding leasing real estate.

None.

Item 2.

PropertiesProperties.

At December 31, 2010,2012, we owned or had interests in 146157 properties, totaling approximately 39.944.4 million net rentable square feet, including fivenine properties under construction totaling approximately 2.02.8 million net rentable square feet. In addition, we had structured parking for approximately 40,66446,833 vehicles containing approximately 13.715.9 million square feet. Our properties consisted of (1) 140149 office properties, including 121132 Class A office buildings, including threeeight properties under construction, and 1917 properties that support both office and technical uses, (2) threefour retail properties, (3) one hotel and (4) twothree residential properties (both(one of which areis under construction). In addition, we own or control 513.3509.3 acres of land for future development. The table set forth below shows information relating to the properties we owned, or in which we had an ownership interest, at December 31, 2010.2012. Information relating to properties owned by the Value-Added Fund is not included in our portfolio information tables or any other portfolio level statistics because the Value-Added Fund invests in assets within our existing markets that havehad deficiencies in property characteristics which provideprovided an opportunity to create value through repositioning, refurbishment or renovation. We therefore believe including such information in our portfolio tables and statistics would render the portfolio information less useful to investors. Information relating to the Value-Added Fund is set forth separately below.