The Karlsruhe Stadtbahn is a German tram-train system combining tram lines in the city of Karlsruhe with railway lines in the surrounding countryside, serving the entire region of the middle upper Rhine valley and creating connections to neighbouring regions. The Stadtbahn combines an efficient urban railway in the city with an S-Bahn, overcoming the boundary between trams and trains. Its logo does not include the green and white S-Bahn symbol used in other German suburban rail systems and the symbol is only used at stops and stations outside the inner-city tram-operation area.

A tram-train is a type of light rail vehicle that both meets the standards of a light rail system, and also national mainline standards. Tramcars are adapted to be capable of running on streets like an urban tramway but also be permitted operation alongside mainline trains. This allows services that can utilise both existing urban light rail systems and mainline railway networks and stations. It combines the urban accessibility of a tram or light rail with a mainline train's greater speed in the suburbs.