San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is a major international airport located 13 miles (21 km) south of downtown San Francisco, California, United States, near the cities of Millbrae and San Bruno in unincorporated San Mateo County. It is often referred to as SFO. The airport has flights to points throughout North America and is a major gateway to Europe and Asia.

It is the largest airport in the San Francisco Bay Area and the second busiest airport in California after Los Angeles International Airport. In 2009 San Francisco International Airport was the tenth busiest in the United States and the twentieth largest airport in the world, by passenger count. It is the sixth largest hub of United Airlines. It also serves as Virgin America's principal base of operations. It is the sole maintenance hub of United Airlines. SFO has numerous passenger amenities, including a range of food and drink establishments, shopping, baggage storage, public showers, a medical clinic, and assistance for lost or stranded travelers and military personnel. It has the Louis A. Turpen Aviation Museum, the San Francisco Airport Commission Aviation Library, and permanent and temporary art exhibitions in several places in the terminals. Free Wi-Fi is available to the public in most of the terminal area.