Federal Office Building, Renaissance Revival federal building in United Nations Plaza, San Francisco, United States.

The 50 United Nations Plaza Federal Office Building is a six-story federal building on United Nations Plaza between Hyde and McAllister Streets, designed by Arthur Brown, Jr. and completed in 1936. Its granite-faced south facade has a rusticated two-story base and a colonnade of detached two-story Doric columns above, with a balustraded attic. The main entrance's three arches are topped by medallions: a carved shield on the central keystone, eagles with olive branches on the flanking ones.

After the 1906 earthquake destroyed thousands of buildings, construction of this structure completed the San Francisco Civic Center plan as part of the city's recovery. The building was part of a broader effort to rebuild destroyed areas with new, modern structures.

The building's name comes from United Nations Plaza, the one-acre pedestrian area laid out beside it in 1975 by landscape architect Lawrence Halprin. The plaza honours the signing of the UN Charter in the nearby Veterans Building on 26 June 1945. The building itself was vacated in 2007 and taken over by the General Services Administration in 2013 after renovation.

The building occupies the block bounded by United Nations Plaza and Hyde, McAllister and Leavenworth streets, with its main entrance of three arched openings at the center of the south elevation facing the plaza. The south facade's colonnade of two-story Doric columns and the carved mascarons on the exterior are visible from the public plaza. The building was vacated in 2007 and taken over by the U.S. General Services Administration in 2013 after renovation.

The mascarons carved on the exterior carry horticultural headpieces: corn, wheat, cattails and oak leaves. The main entrance's three arches are topped by medallions, the central one with a carved shield and the flanking ones with eagles holding olive branches.