San Francisco 4th and King Street station, also known as the Caltrain Depot, is a train station in the SoMa district of San Francisco, California. It is presently the northern terminus of the Caltrain commuter rail line serving the San Francisco Peninsula and Santa Clara Valley. It is also the eastern terminus of the N Judah and E Embarcadero, as well as a stop along the T Third Street of the Muni network. The station is additionally the projected terminus for the first phase of the California High-Speed Rail project and a station once Phase 2 is completed.

Caltrain is a California commuter rail line serving the San Francisco Peninsula and Santa Clara Valley. The southern terminus is in San Jose at Tamien station with weekday rush hour service running as far as Gilroy. The northern terminus of the line is in San Francisco at 4th and King Street. Caltrain has 28 regular stops, one limited-service weekday-only stop, one weekend-only stop (Broadway), and one football-only stop (Stanford). While average weekday ridership in 2019 exceeded 63,000, impacts of the COVID-19 pandemic have been significant: in August 2022, Caltrain had an average weekday ridership of 18,600 passengers.