The Forchbahn (German for "Forch railway") is a 1,000 mm (3 ft 3 3⁄8 in) gauge narrow-gauge (Schmalspurbahn) light railway in the canton of Zürich, linking central Zürich (Zürich Stadelhofen railway station) to the eastern suburbs near Esslingen via Forch. The name is often abbreviated to just FB, which also appears on the trains. Locals call the train "Auntie Frieda" ("Tante Frieda").
It opened on November 27, 1912, with the trip taking 67 minutes. By 2002, this had been reduced to just 36 minutes, partly due to new rolling stock.
Between 1973 and 1976 a tunnel was built under Zumikon to reduce noise pollution in the town. The Forchbahn has two adjacent underground stops: Zumikon and Maiacher.
In 1976, a regular 15-minute train frequency was introduced. This is now standard throughout the daytime between Zürich and Forch. During rush hours, the 15-minute frequency is extended to the whole route. There is now a night Forchbahn as well with an hourly frequency, from 1 AM to 4 AM.
Projected extensions to Zürich Hauptbahnhof and Wetzikon were under consideration as early as 1979. However, they have yet to become reality.
In 1990, the line was added to the ZVV transportation network. Forchbahn is providing the line S18 of the S-Bahn Zürich, sharing the tracks between Zürich Stadelhofen station and Rehalp with Zürich trams.