San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is the primary international airport serving the San Francisco Bay Area in California, United States. It is located in San Mateo County.

SFO is the largest airport in the San Francisco Bay Area and the second-busiest in California, after Los Angeles International Airport (LAX). In 2023, it was the fourteenth-busiest airport in the United States and the 30th-busiest in the world by passenger count. It is the fifth-largest hub for United Airlines, functioning as the airline's primary transpacific gateway, and is a major maintenance hub. It also serves as a hub for Alaska Airlines.

The airport is owned and operated by the City and County of San Francisco and has a mailing address with a ZIP code assigned to San Francisco. Between 1999 and 2004, the San Francisco Airport Commission operated city-owned SFO Enterprises Inc to oversee its business purchases and operations of ventures.