The San Francisco Bay is a gulf of the Pacific Ocean in the US state of California, surrounded by a contiguous region known as the San Francisco Bay Area, dominated by the big cities San Francisco, Oakland, and San Jose.

San Francisco Bay is spanned by five bridges: the Golden Gate Bridge (which was the largest suspension bridge ever built at the time of its construction), the Richmond-San Rafael Bridge, the San Francisco-Oakland Bay Bridge, the Hayward-San Mateo Bridge and the Dumbarton Bridge.

The southern part of the San Francisco Peninsula including the city of San Jose is known as the Silicon Valley for its high concentration of high-tech, semiconductor and computer-related industry.