The Frankfurt U-Bahn is a Stadtbahn (premetro) system serving Frankfurt, Germany. Together with the Rhine-Main S-Bahn and the tram network, it forms the backbone of the public transport system in Frankfurt. Its name derives from the German term for underground railway, Untergrundbahn. Since 1996, the U-Bahn has been owned and operated by Stadtwerke Verkehrsgesellschaft Frankfurt am Main (VGF), the public transport company of Frankfurt, and is part of the Rhein-Main-Verkehrsverbund (RMV) transport association. The licence contract is up to 31 December 2031 and is renewable. The contracting authority of VGF is the municipal transport company traffiQ.