San Francisco International Airport (SFO), though located 13 miles (21 km) south of the city in San Mateo County, is under the jurisdiction of the City and County of San Francisco. It is a hub for United Airlines, its largest tenant, and the decision by Virgin America to base its future operations out of SFO reverses the trend of low-cost carriers opting to bypass SFO for Oakland and San Jose. SFO is an international gateway, with the largest international terminal in North America.

The airport is built on a landfill extension into the San Francisco Bay. During the economic boom of the late 1990s, when traffic saturation led to frequent delays, it became difficult to respond to calls to relieve the pressure by constructing an additional runway as that would have required additional landfill. Such calls subsided in the early 2000s as traffic declined, and, in 2005, SFO was the 14th busiest airport in the United States and 23rd largest in the world, handling 32.8 million passengers.

San Francisco is renowned for its months-long episodes of fog, steep rolling hills, the eclectic mix of Victorian and modern architecture, and its peninsular location surrounded on three sides by the Pacific Ocean and San Francisco Bay. Famous hallmarks and landmarks include the Golden Gate Bridge, Alcatraz Island, the cable cars, the Transamerica Pyramid, and Chinatown.