San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is the primary international airport for the San Francisco Bay Area in the U.S. state of California. Owned and operated by the City and County of San Francisco, the airport has a San Francisco mailing address and ZIP Code, although it is situated in an unincorporated area of neighboring San Mateo County, approximately 12 miles (19 km; 10 nmi) southeast of San Francisco.

SFO is the largest airport in the Bay Area and the second-busiest in the US State of California, following Los Angeles International Airport (LAX). In 2023, it ranked as the 13th-busiest airport in the United States and the 29th-busiest in the world by passenger traffic. It is a hub for United Airlines, acting as the airline's primary transpacific gateway, and as a major maintenance facility. Additionally, SFO functions as a hub for Alaska Airlines.