One Bush Plaza, Modern skyscraper in Financial District, San Francisco, United States.

One Bush Plaza, also known as the Crown Zellerbach Building, is a 20-story, 308-foot (94 m) office tower at Bush and Battery Streets in San Francisco's Financial District. Designed by Skidmore, Owings & Merrill and completed in 1959, it is freestanding and occupies an entire city block. Its facades are grids of teal-blue glass panes held in closely spaced dark vertical mullions, rising to a flat roofline.

The building was completed in 1959 and represented the first major construction project in downtown San Francisco following the Great Depression of the 1930s. This opening symbolized economic recovery and the beginning of a new phase of urban growth for the city.

The Crown Zellerbach name survives in the building's alternative title, a reminder of the forest-products firm that commissioned it. Skidmore, Owings & Merrill's design won the 1959 Office of the Year Award of Merit from Administrative Management Magazine, and in 1997 the American Institute of Architects' California Council gave it its 25 Year Award.

The building sits at the corner of Bush Street and Battery Street, making it easy to reach on foot from other parts of the Financial District. The location offers good transit connections and sits near public transportation and other office buildings.

One Bush Plaza occupies an entire city block and stands free of neighbouring structures, so it can be seen from all four sides. It was also the first International Style building in San Francisco, completed shortly after New York's Lever House and Seagram Building. The design by Skidmore, Owings & Merrill drew controversy for facing Bush Street rather than Market Street, then in decline.