The East Bay Electric Lines were a unit of the Southern Pacific Railroad that operated electric interurban-type trains in the East Bay region of the San Francisco Bay Area. Beginning in 1862, the SP and its predecessors operated local steam-drawn ferry-train passenger service in the East Bay on an expanding system of lines, but in 1902 the Key System started a competing system of electric lines and ferries. The SP then drew up plans to expand and electrify its system of lines and this new service began in 1911. The trains served the cities of Berkeley, Albany, Emeryville, Oakland, Alameda, and San Leandro transporting commuters to and from the large Oakland Pier and SP Alameda Pier. A fleet of ferry boats ran between these piers and the docks of the Ferry Building on the San Francisco Embarcadero.

The Key System was a privately owned company that provided mass transit in the cities of Oakland, Berkeley, Alameda, Emeryville, Piedmont, San Leandro, Richmond, Albany, and El Cerrito in the eastern San Francisco Bay Area from 1903 until 1960, when it was sold to a newly formed public agency, AC Transit. The Key System consisted of local streetcar and bus lines in the East Bay, and commuter rail and bus lines connecting the East Bay to San Francisco by a ferry pier on San Francisco Bay, later via the lower deck of the Bay Bridge. At its height during the 1940s, the Key System had over 66 miles (106 km) of track. The local streetcars were discontinued in 1948 and the commuter trains to San Francisco were discontinued in 1958. The Key System's territory is today served by BART and AC Transit bus service.