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 large cities such as San Francisco, Oakland, and San Jose, along with smaller urban and rural areas. Overall, the Bay Area consists of nine counties, 101 cities, and 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 almost 7 million people. It is one of the wealthiest regions in the United States, according to the United States Census Bureau. The area has the highest median household income in the nation at over $65,000. The Bay Area hosts many cities, towns, military bases, airports, and associated regional, state, and national parks, connected by a massive network of roads, highways, railroads, bridges, tunnels and commuter rail. The combined urban area of San Francisco and San Jose is the 47th largest urban area in the world.

While San Jose, California is 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.

In addition to having the highest median household income in the nation, the Bay Area has the highest 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.