Noncontrolling interests relate to the interests in the Operating Partnership not owned by the Company and interests in property partnerships not wholly-owned by the Company. As of September 30, 2011, the noncontrolling interests consisted of 17,037,553 OP Units, 1,603,205 LTIP Units, 400,000 2011 OPP Units and 1,113,044 Series Two Preferred Units (or 1,460,688 OP Units on an as converted basis) held by parties other than the Company.

Noncontrolling Interest—Redeemable Preferred Units of the Operating Partnership

The Preferred Units at September 30, 2011 consisted solely of 1,113,044 Series Two Preferred Units, which bear a preferred distribution equal to the greater of (1) the distribution which would have been paid in respect of the Series Two Preferred Unit had such Series Two Preferred Unit been converted into an OP Unit (including both regular and special distributions) or (2) 6.00% per annum on a liquidation preference of $50.00 per unit, and are convertible into OP Units at a rate of $38.10 per Preferred Unit (1.312336 OP Units for each Preferred Unit). The holders of Series Two Preferred Units have the right to require the Operating Partnership to redeem their units for cash at the redemption price of $50.00 per unit on 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 on May 12, 2009, May 12, 2010 and May 12, 2011, although no holder exercised such right. On May 14, 2013 and May 12, 2014, the Company also has the right, subject to certain conditions, to redeem Series Two Preferred Units for cash or to convert into OP Units any Series Two Preferred Units that are not redeemed when they are eligible for redemption.

On February 15, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.75616 per unit. On May 16, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.73151 per unit. On August 15, 2011, the Operating Partnership paid a distribution on its outstanding Series Two Preferred Units of $0.75616 per unit.

The following table reflects the activity of the noncontrolling interests—redeemable preferred units of the Operating Partnership for the nine months ended September 30, 2011 and 2010 (in thousands):

Noncontrolling Interest—Common Units of the Operating Partnership

During the nine months ended September 30, 2011, 2,442,407 OP Units were presented by the holders for redemption (including 58,213 OP Units issued upon conversion of LTIP Units) and were redeemed by the Company in exchange for an equal number of shares of Common Stock.

At September 30, 2011, the Company had outstanding 400,000 2011 OPP Units (See Note 10). Prior to the measurement date on January 31, 2014, 2011 OPP Units will be entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of 2011 OPP Units, both vested and unvested, that 2011 OPP award recipients have earned, if any, based on the establishment of an outperformance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit.

On February 5, 2011, the measurement period for the Company's 2008 OPP Awards expired and the Company's TRS performance was not sufficient for employees to earn and therefore become eligible to vest in any of the 2008 OPP Awards. Accordingly, all 2008 OPP Awards were automatically forfeited and the Operating Partnership repaid employees an amount equal to $0.25 (which is equal to what they paid upon acceptance of the award) multiplied by the number of 2008 OPP Awards previously received.

On January 28, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2008 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on December 31, 2010. On April 29, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on March 31, 2011. On July 29, 2011, the Operating Partnership paid a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit, and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, to holders of record as of the close of business on June 30, 2011. On September 16, 2011, Boston Properties, Inc., as general partner of the Operating Partnership, declared a distribution on the OP Units and LTIP Units in the amount of $0.50 per unit and a distribution on the 2011 OPP Units in the amount of $0.05 per unit, in each case payable on October 31, 2011 to holders of record as of the close of business on September 30, 2011.

The Series Two Preferred Units may be converted into OP Units at the election of the holder thereof at any time. A holder of an OP Unit may present such OP Unit to the Operating Partnership for redemption at any time (subject to restrictions agreed upon at the time of issuance of OP Units to particular holders that may restrict such redemption right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, the Operating Partnership must redeem such OP Unit for cash equal to the then value of a share of common stock of the Company. The Company may, in its sole discretion, elect to assume and satisfy the redemption obligation by paying either cash or issuing one share of Common Stock. The value of the OP Units (not owned by the Company and including LTIP Units assuming that all conditions have been met for the conversion thereof) and Series Two Preferred Units (on an as converted basis) had all of such units been redeemed at September 30, 2011 was approximately $1.66 billion and $130.1 million, respectively, based on the closing price of the Company's common stock of $89.10 per share on September 30, 2011.

The noncontrolling interests in property partnerships consist of the outside equity interest in ventures that are consolidated with the financial results of the Company because the Company exercises control over the entities that own the properties. The equity interests in these ventures that are not owned by the Company, totaling approximately $(1.0) million at September 30, 2011 and approximately $(0.6) million at December 31, 2010, are included in Noncontrolling Interests—Property Partnerships on the accompanying Consolidated Balance Sheets.