Pan American Union Building

It is located at 17th Street N.W. between C Street N.W. and Constitution Avenue, Northwest, Washington, D.C.

Pan American Union Building
U.S. National Register of Historic Places
U.S. National Historic Landmark
Organization of American States headquarters building, with the Statue of Isabella I in front (2015)
Location	17th Street NW between C Street NW and Constitution Avenue, NW. Washington, D.C.
Coordinates	38°53′34″N 77°02′25″W / 38.89288°N 77.04026°W / 38.89288; -77.04026
Built	1908–1910
Architect	Paul P. Cret and Albert Kelsey
NRHP reference No.	69000298, 10000625
Significant dates
Added to NRHP	4 June 1969
Designated NHL	13 January 2021

On the former site of the John Peter Van Ness Mansion. The cornerstone was laid on May 11, 1908, by Theodore Roosevelt, Elihu Root, and Andrew Carnegie (who largely financed the building's construction), and the building was dedicated on April 26, 1910.

In 1919, the initial meeting of the International Labour Organization was held in the building.

Between 1921 and 1922, the building was used for committee and subcommittee hearings throughout the Washington Naval Conference while closely guarded by marines with fixed bayonets.

The building was added to the National Register of Historic Places in 1969, and was designated a National Historic Landmark in 2021, for its architecture and its role in international diplomacy.