1800 Massachusetts Avenue is located in historic Dupont Circle in Washington, DC and houses the corporate office of SEIU.

Constructed in 1979, 1800 Massachusetts Avenue underwent a major three-phase renovation commencing in 2003 and completed in the summer of 2007. Anchor Clients include SEIU and Clutch. Total rentable office and retail square footage is 198, 309. The property includes a manned parking garage, which operates under a management agreement by Federal Garage Management. The Retail Client includes Un je ne sais Quoi.