Flood Building, Historic office building at Market Street and Powell Street, San Francisco, United States.

The Flood Building is a 12-story steel-frame high-rise at 870 Market Street, on the corner of Powell Street beside the cable car turntable. Designed by Albert Pissis, it has a grey Colusa sandstone façade in Baroque Revival style with deep-chiselled windows. A red-marble-columned lobby runs through to Ellis Street, and wedge-shaped office floors surround a lightwell.

The site held Baldwin's Hotel and Theatre, destroyed by fire in 1898, before James L. Flood bought it and built a tribute to his father, Comstock Lode millionaire James Clair Flood. Albert Pissis designed the structure, which opened in 1904 as San Francisco's largest building. It survived the 1906 earthquake and fire, though restoring the interior took two years. In 1950 Woolworth's planned a three-story replacement, but the Navy requisitioned the building during the Korean War and returned it to the family in 1953.

The building's name honours James Clair Flood, the Comstock Lode millionaire, through a structure his son James L. Flood built as a tribute. The Pinkerton Detective Agency kept an office on the third floor, where novelist Dashiell Hammett worked as an operative and later placed his fictional Continental Detective Agency. From 1952 to 1993 the Woolworth's at its base was the largest in the chain.

The building sits in a central downtown location with easy public transit access and nearby shops and restaurants. Visitors can view the public lobby and corridors without entering private office spaces.

Writer Dashiell Hammett worked as a detective in this building before becoming famous, and the experience directly inspired his novel The Maltese Falcon set in the city. The corridors and offices helped shape his vision of the crime story.