A tram-train is a light-rail public transport system where trams run through from an urban tramway network to main-line railway lines which are shared with conventional trains. This combines the tram's flexibility and accessibility with a train's greater speed, and bridges the distance between a main railway stations and a city centre.

The tram-train concept was pioneered with the Karlsruhe model in Germany, and has since been adopted on projects such as the RijnGouweLijn in the Netherlands, at Mulhouse in France and in Kassel and Saarbrücken in Germany.

The tram-train is a type of interurban, according to George W. Hilton and John F. Due's definition.^{[citation needed]}

Most tram-trains are standard gauge, which facilitates sharing track with main-line trains. Exceptions include Alicante Tram and Nordhausen which are metre gauge, and the 950 mm gauge Sassari Tram-train.

Tram-train vehicles are dual-equipped to suit the needs of both tram and train operating modes, with support for multiple electrification voltages if required and safety equipment such as train stops and other railway signalling equipment. The Karlsruhe and Saarbrücken systems use ‘PZB’ or ‘Indusi’ automatic train protection, so that if the driver passes a signal at stop the emergency brakes are applied.