Frankfurt U-Bahn, Light rail network in Frankfurt, Germany.

The Frankfurt U-Bahn is a Stadtbahn (premetro) system with nine lines (U1–U9) and 84 stations on 64.85 km of track, about 59% underground. Three inner-city tunnels form trunk routes A, B and C; route D is only partly built. Above ground, trains run on separated embankments, cuttings and some street-running sections. Platforms vary: some have salmon-toned floors with yellow safety stripes and grey columns, others polished brown floors, brown-clad pillars and "Ausgang" signs.

Operations began in 1968, launching a new era of mass transit for the rapidly growing metropolitan region. Since then, the network has continuously expanded and become the backbone of Frankfurt's urban mobility.

The name U-Bahn comes from Untergrundbahn, German for underground railway, though only about 59% of the track runs below ground. The system is run by the city-owned VGF under the traffiQ authority and has been part of the Rhein-Main-Verkehrsverbund fare network since 1995. On platforms, look for the "Ausgang" signs with arrows pointing to the exits.

The network has 84 stations on nine lines over 64.85 km; eight lines pass through the city centre, while U9 bypasses it. About 59% of the track runs underground, with above-ground sections in the suburbs. The U8 and U9, added on 12 December 2010, serve the university campus and the Riedberg development.

The U9, added on 12 December 2010 with the U8, was the first line in the network not to touch the city centre, serving the university campus and the Riedberg development. The system is classed as a Stadtbahn rather than a full U-Bahn: the third construction phase that would have separated it entirely from road traffic was never completed.