The North Bay is a subregion of the San Francisco Bay Area, in the U.S. state of California. It is by far the least populous and urbanized part of the Bay Area. It consists of Marin, Sonoma, Napa, and Solano Counties. It is, unusally for a major metropolitan area, still highly agricultural in character. Most famously, the California wine country (consisting of the neighboring Sonoma and Napa Valleys) is located in the North Bay. Historically, it is also dairy farming region. Although the growth of the wine industry has slowly edged out the dairy industry, it is still common to see cows grazing on the hillsides of Sonoma County in particular.

The North Bay is connected to San Francisco by the Golden Gate Bridge, and to the East Bay by the Richmond-San Rafael Bridge (usually called simply the Richmond Bridge) and the Benicia Bridge, which crosses the San Pablo Bay between Benicia and Martinez. It is the only part of the Bay Area not to be served by Bay Area Rapid Transit (BART), as the logisitic and finacial difficulties involved in building a transbay tube either to the south or east would not be inconsequential, and the population is not large enough to warrant it.

The Bear Flag Revolt took place in the town of Sonoma, which is also the location of the last of the California Missions. General Mariano Vallejo, the last secretary to the Governor of California before its annexation to the United States kept his home in Sonoma, and his ranch, now a National Historic Location was located in nearby Petaluma.

The largest city in the North Bay is Santa Rosa.