The Market Street Railway Company was a commercial streetcar and bus operator in San Francisco. The company was named after the famous Market Street of that city, which formed the core of its transportation network. Over the years, the company was also known as the Market Street Railroad Company, the Market Street Cable Railway Company and the United Railroads of San Francisco. Once the largest transit operator in the city, the company folded in 1944 and its assets and services were acquired by the city-owned San Francisco Municipal Railway. Many of the former routes continue to exist into the 2020s, but served by buses.

Market Street is a major thoroughfare in San Francisco, California. It begins at The Embarcadero in front of the Ferry Building at the northeastern edge of the city and runs southwest through downtown, passing the Civic Center and the Castro District, to the intersection with Portola Drive in the Twin Peaks neighborhood. Beyond this point, the roadway continues into the southwestern quadrant of San Francisco. Portola Drive extends south to the intersection of St. Francis Boulevard and Sloat Boulevard, where it continues as Junipero Serra Boulevard.