The British Rail Class 373 or TGV TMST, sometimes referred to as Eurostar e300, is a French designed and Anglo-French built electric multiple unit train that is used for Eurostar international high-speed rail services from the United Kingdom to France and Belgium through the Channel Tunnel. Part of the TGV family, it was built with a smaller cross-section to fit the smaller loading gauge in Britain, was originally capable of operating on the UK third rail network, and has extensive fireproofing in case of fire in the tunnel.

Known as the TransManche Super Train (TMST) or Cross-channel Super Train before being introduced in 1993, the train is designated Class 373 under the British TOPS classification system and series 373000 TGV in France. It was built by the French company GEC-Alsthom. Since the introduction of the new Class 374 e320 units from Siemens in 2015, refurbished versions of the Class 373 or TGV-TMST sets have been officially referred to as e300 by Eurostar to distinguish them from the new Velaro fleet