The first municipally owned streetcars take to the streets in San Francisco.

The San Francisco Municipal Railway is the primary public transit system within San Francisco, California. It operates a system of bus routes, the Muni Metro light rail system, three historic cable car lines, and two historic streetcar lines. Previously an independent agency, the San Francisco Municipal Railway merged with two other agencies in 1999 to become the San Francisco Municipal Transportation Agency (SFMTA). In 2018, Muni served 46.7 square miles (121 km²) with an operating budget of about $1.2 billion. Muni is the seventh highest-ridership transit system in the United States, with 145,641,700 rides in 2024, and the second highest in California after the Los Angeles County Metropolitan Transportation Authority.

A tram is an urban rail transit in which vehicles, whether individual railcars or multiple-unit trains, run on tramway tracks on urban public streets; some include segments on segregated right-of-way. The tramlines or tram networks operated as public transport are called tramways or simply trams/streetcars. Because of their close similarities, trams are commonly included in the wider term light rail, which also includes systems separated from other traffic.

San Francisco, officially the City and County of San Francisco, is a commercial, financial, and cultural center of Northern California. With a population of 827,526 residents as of 2024, San Francisco is the fourth-most populous city in the U.S. state of California and the 17th-most populous in the United States. San Francisco has a land area of 46.9 square miles at the upper end of the San Francisco Peninsula and is the fifth-most densely populated U.S. county. Among U.S. cities proper with over 250,000 residents, San Francisco is ranked first by per capita income and sixth by aggregate income as of 2023. San Francisco anchors the 13th-most populous metropolitan statistical area in the U.S., with almost 4.6 million residents in 2023. The larger San Jose–San Francisco–Oakland combined statistical area, the fifth-largest urban region in the U.S., had a 2023 estimated population of over nine million.