In San Francisco, these vehicles are also known as "trolley coaches", a term that was the most common name for trolleybuses in the United States in the middle decades of the 20th century.

[8] Long a hub of streetcar development, San Francisco already had much of the overhead wire infrastructure necessary to deploy trolleybus service on existing city streets.

By early August of that year, the Market Street Railway Company (MSRy), successor to the URR, applied to the State Railroad Commission to operate the first trackless trolley system in California;[11] permission was granted by August 30,[12] and the first trolleybus service started on October 6, 1935, using 9 coaches built by Brill.

That route initially ran along 18th from Guerrero to Douglass before being extended to Frederick and Ashbury including a sharp hairpin turn on the lower slopes of Twin Peaks at Market and Clayton by May 1894.

33 streetcar operated between Third & Harrison (Downtown) and Waller & Stanyan (Golden Gate Park),[11] a round trip of 10.2 miles (16.4 km).

[14] After riding the trackless trolley, the editor of the San Bernardino Sun published a rumor that all streetcar service would eventually be replaced with trolleybuses.

[16] The R-Howard line was introduced specifically so that Muni could undercut MSRy's prices on its parallel routes on Mission Street.

[9]: 42  The 35-Howard line originally ran from the Ferry Building along Howard, South Van Ness, and 24th to that street's intersection with Rhode Island.

Those five lines ran 1940s-era PCC streetcars through the 1970s and were subsequently converted to the Muni Metro light rail system using Boeing-Vertol SLRVs.

Analysis has found that maintenance and expansion of the trolleybus network in San Francisco could be the fastest and cheapest way for Muni to comply with the mandate and decarbonize its fleet.

[21] While many municipalities further converted their trolleybus systems to diesel buses during the middle of the 20th century, San Francisco maintained trolleybuses due to their ability to climb the city's notably steep grades and because electricity was available at extremely low cost from the city-owned O'Shaughnessy Dam.

The overwhelming popularity of the new F line allowed Muni to reduce the frequency of and then discontinue the 8-Market, though the overhead wires remain in place.

[25]: 5 Trolleybuses operate on the following Muni routes:[26] Since the start of service in 1935 (on the Market Street Railway system), the San Francisco trolleybus system fleet has included vehicles built by many different manufacturers, including the J. G. Brill Company, the St. Louis Car Company, Marmon-Herrington, Twin Coach, Flyer Industries (now New Flyer), and Electric Transit.

[35] Market Street Railway was the first transit organization in San Francisco to run trackless trolleys, using nine coaches built by Brill in 1935 for the 33 line, numbered 51–59.

[38] In addition, Muni ordered 90 trolleybuses from Twin Coach comparable to the Medium Marmons in 1949 (Model 44TTW, numbered 570–659, 44 seats).

[39] The final expansion of the trolleybus fleet in the 1950s was accomplished by purchasing 40 48-seat coaches from the St. Louis Car Company in the early 1950s.

By 1995, the MDBF had fallen to just 600 mi (970 km), and each breakdown was taking an average of 41⁄4 days to fix, often compounded by the unavailability of parts for the E800s, which were nearly 20 years old at that point.

[24] In addition, a number of incidents where poles had detached from the wires and subsequently struck pedestrians and vehicles gained publicity at the time.

[25][43] Muni was the only customer for the E60 trolleybus variant of the New Flyer Galaxy; a prototype was built in 1992 and numbered 7000 for evaluation before the larger purchase was completed.

[52]: 5 During testing, the new ETI trolleybuses were compared to a "luxury car" by one driver, and touted features included a new pneumatic system to raise and lower trolley poles and an on-board battery to allow off-wire operation for up to 2+1⁄2 mi (4.0 km).

[54] The ETI trolleybuses were assembled at Pier 15;[51] manufacturing started in the Czech Republic with frames, motors and controls, continued in Hunt Valley, Maryland, where the body, paint, under-flooring and wiring were added, and finished in San Francisco.

[55] The manufacturing activities were designed to meet "Buy America" regulations required for vehicles procured using federal assistance.

[26][57][25]: 5–6  Parts for the ETI trolleybuses needed to be shipped from the Czech Republic, increasing the time spent out of service.

[59][60] By 2017, the 14TrSF fleet had aged to a point where they were collectively responsible for nearly half of all Muni service delays resulting from mechanical failures.

[61][62] In 2013, the SFMTA adopted plans for an eventual one-for-one replacement of the existing trolleybus fleet in a joint procurement with King County Metro and New Flyer over technical specifications and pricing.

MSRy merged with Muni in 1944, and in the years since then the trolleybus fleet has also included vehicles built by the St. Louis Car Company, Marmon-Herrington, Twin Coach, and Flyer Industries.