The TGV (train à grande vitesse, French for "high-speed train") is France's high-speed rail service developed by GEC-Alsthom (now Alstom) and SNCF, the French national rail operator, and operated primarily by SNCF. Following the inaugural TGV service between Paris and Lyon in 1981, the TGV network, centred on Paris, has expanded to connect cities across France and in adjacent countries. It holds the record for the fastest wheeled train, having reached 574.8 km/h (357 mph) on 3 April, 2007, and also holds the world's highest average speed for a regular passenger service. TGV is a registered trademark of SNCF.

The success of the first line led to an expansion of the network, with new lines built in the south, west, north and east of the country. Eager to emulate the success of the French network, neighbouring countries such as Belgium, Italy, Spain and Germany built their own high-speed lines. TGVs link with Switzerland through the French network, with Belgium, Germany and the Netherlands through the Thalys network, and the Eurostar network links France and Belgium with the United Kingdom. Several lines are planned, including extensions within France and to surrounding countries. Towns such as Tours have become a part of a "TGV commuter belt".

TGV trainsets travel at up to 320 km/h (200 mph) in commercial use. A specially modified trainset reached 574.8 km/h (357 mph) on test runs. Its high speed, almost equal to that of prototype maglev trains, is made possible through the use of specially-designed LGVs (lignes à grande vitesse, high-speed lines) without sharp curves and with high-powered electric motors, low axle weight, articulated carriages and in-cab signalling (eliminating the need for drivers to view lineside signals at high speed).

TGV trainsets are manufactured primarily by Alstom, now often with the involvement of a subcontractor, such as Bombardier. Except for a small series of TGVs used for postal freight between Paris, Lyon and Provence, the TGV is primarily a passenger service. Trains derived from TGV designs operate in South Korea (KTX), Spain (AVE) and USA (ACELA Express).

Travel by TGV has largely replaced air travel between connected cities, due to shorter travel times (especially for trips taking less than three hours), reduced check-in, security and boarding formalities, and the convenient location of stations in the hearts of cities. The TGV is a very safe mode of transport; whilst there have been accidents, there has never been a fatality while travelling at high speed.