The Régie Autonome des Transports Parisiens (RATP) is the major transit authority responsible for public transportation in Paris and its environs. Its operational divisions include the Paris Metro system, the RER, an extensive bus system, and two light rail lines.
The RATP was created on March 21, 1948, by combining the assets of the Compagnie du Chemin de Fer Métropolitain de Paris (CMP), which operated the Paris Metro, and the Société des Transports en Commun de la Région Parisienne (STCRP), which operated the city's bus system.
Earlier, the CMP had absorbed the Société du Chemin de Fer Electrique Nord-Sud de Paris in 1930 and the Ligne de Sceaux in 1937. The STCRP had been created on January 1, 1921 by the merger of about half a dozen independent bus and streetcar operators in the Paris area. By the time the STCRP was merged into the RATP, all its streetcars had been replaced by bus routes.
Ironically, there are now projects of creating new light rail lines, most notably as a replacement for the Petite Ceinture bus line going over the Marshals' Boulevard.