San Francisco, officially the City and County of San Francisco, is a consolidated city-county located in California, United States. It sits on a small square of land seven miles on each side, sandwiched between the San Francisco Bay and the Pacific Ocean at the Golden Gate. As the fourth-most populous city in California and the 17th-most populous in the United States, it serves as the centerpiece of the San Francisco Bay Area, one of the most economically productive large urban areas in the world.

Prior to European settlement, the area was inhabited by the Yelamu Ohlone. On June 29, 1776, settlers from New Spain established the Presidio of San Francisco and Mission San Francisco de Asís, both named for Francis of Assisi. The California gold rush of 1849 brought rapid growth, making it the largest city on the West Coast at the time. In 1856, it became a consolidated city-county, and after being largely destroyed by the 1906 earthquake, it was quickly rebuilt.

The city is known for its steep rolling hills, eclectic mix of architecture, and varied neighborhoods including Chinatown and the Mission District. Notable landmarks include the Golden Gate Bridge, cable cars, and Alcatraz. The cultural center of northern California features a mixture of scenic beauty and unique culture, with districts ranging from the crowded streets of Chinatown to the Castro, reflecting great ethnic and cultural diversity across the city.

San Francisco attracts millions of visitors annually, drawn by its mild climate, liberal activism history, and vibrant arts scene. It is home to numerous educational and cultural institutions such as the University of California, San Francisco, the de Young Museum, and the San Francisco Symphony. The city also hosts two major league sports teams, the Giants and the Warriors, and has a rich history involving the beatnik and hippie countercultures.

The population was 808,988 as of 2023. The economy is spurred by leading universities and sectors including high-tech, healthcare, finance, and professional services, with major companies like Salesforce, Uber, and Airbnb headquartered there. San Francisco International Airport (SFO) is one of the world's busiest airports, while a light rail and bus network connects the city with the wider region via BART and Caltrain systems.