The San Francisco Bay Area, commonly known as the Bay Area or the Bay, is a geographically and ethnically diverse metropolitan region that surrounds the San Francisco and San Pablo bays in Northern California. It encompasses the cities of San Jose, San Francisco, and Oakland. It also includes the smaller urban and rural areas of the North Bay. Overall, the Bay Area consists of nine counties, 101 cities, and comprises 7,000 square miles. The nine counties are Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma. As of July 2006, the Bay Area is home to 7.2 million people, making it the fifth most populous metropolitan area in the United States, with the majority of the growth due to international immigration. The Bay Area comprises many cities, towns, military bases, airports, and associated regional, state, and national parks sprawled over nine counties (sometimes defined as ten or eleven counties) and connected by a massive network of roads, highways, railroads, bridges, tunnels and commuter rail.

While San Jose is now the largest city in the Bay Area, having surpassed San Francisco in the 1990 census, for most of its history San Francisco was the area's most populous city. San Francisco remains the focal point and major cultural center in the region . The Bay Area has the highest median household and per capita income of any metropolitan area in the United States and is also one of the most politically liberal areas in the nation. The cost of living is also one of the highest in the nation (San Francisco Chamber of Commerce, 2007).