History:
The airport was first opened on May 7, 1927 on 150 acres (607,000 m²) of cow pasture. The land was leased from prominent local landowner Ogden L. Mills, and was named Mills Field Municipal Airport. It remained Mills Field until 1931, when it was renamed San Francisco Municipal Airport. "Municipal" was replaced by "International" in 1955.

The U.S. Weather Bureau began keeping weather observations at Mills Field in May 1927. The weather records have continued under the National Weather Service, which maintained the Bay Area forecast center in the airport's control tower building until forecasting was moved to Redwood City. The weather station continues to serve as the official observation point for San Francisco; temperature and precipitation data are published nationally in many newspapers.

Starting in 1935, Pan American World Airways used the facility as the terminal for its "China Clipper" flying boat service across the Pacific Ocean. Domestic flights did not begin en masse, however, until World War II, when Oakland International Airport was taken over by the military and its passenger flights were shifted to San Francisco.

After the war, United Airlines took up residence at SFO, using the Pan Am terminal for its flights to Hawaii and other U.S. cities. In 1954, the airport's Central Passenger Terminal opened for passenger service. Jet service to SFO began in the late 1950s: United built a large maintenance facility at San Francisco for its new Douglas DC-8s. In July 1959 the first jetway bridge was installed in the United States. In 1974, a new terminal was built for domestic flights, and the CPT became an international terminal (known today as Terminal 2).