San Francisco International Airport traces its origins to May 7, 1927, when the City and County of San Francisco held a dedication ceremony at Mills Field Municipal Airport, a 150-acre cow pasture in San Mateo County roughly 13 miles south of the city. The airport opened with a single 4,590-foot dirt runway and served just 19 passengers in its first month. Early tenants included Century Pacific Airlines, Maddux Airlines, and Western Air Express. By 1947, the airport had been renamed San Francisco International to reflect a growing roster of Pacific routes, and that same year it crossed the one million annual passenger mark.

Its geographic position on the West Coast made it a natural hub for transpacific service. Japan Airlines arrived in 1954. TWA brought the first commercial jet service with a Boeing 707 in March 1959. A landmark new terminal, dedicated in August 1954 in International Style with a dual-level design separating arrivals from departures, set the architectural tone for decades of expansion. The dot-com boom of the 1990s accelerated growth dramatically, and a $2.4 billion International Terminal Complex opened in December 2000. At 1.8 million square feet, it is the largest international terminal in North America and the largest building in the world constructed on base isolators for earthquake protection. BART rail service reached the airport in June 2003, connecting it directly to downtown San Francisco and the East Bay.

Today SFO is the second-busiest airport in California and a hub for both United Airlines and Alaska Airlines. United operates more transpacific nonstops from SFO than from any of its other hubs, serving Tokyo, Seoul, Beijing, Shanghai, Singapore, and Sydney, among others. Silicon Valley's proximity drives an outsized share of premium corporate travel. The four-terminal layout, including the Harvey Milk Terminal 1, named for the civil rights leader and renovated for sustainability and inclusivity, arranges around a counterclockwise loop connected by a free automated AirTrain.