Alstom SA is a French multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the AGV, TGV, Eurostar, Avelia and New Pendolino high-speed trains, in addition to suburban, regional and metro trains, as well as Citadis trams.

Alsthom (originally as Als-Thom) was formed from a merger between Thomson-Houston Electric Company and the electric engineering division of Société Alsacienne de Constructions Mécaniques in 1928; significant acquisitions included the Constructions Electriques de France (1932), shipbuilder Chantiers de l’Atlantique (1976), and parts of ACEC (Belgium, late 1980s).