Grand Touring (from the Italian word Gran Turismo) racing is the most common form of sports car racing, and is found all over the world, in both international and national series. Historically, Grand Touring cars had to be in series production, but in the 1970s as modifications became more extreme the class split into Group 4 for production based cars and Group 5 for silhouette specials which were essentially pure-bred racing cars with production-lookalike bodies. GT racing gradually fell into abeyance in Europe in the 1980s and 1990s, with silhouette cars continuing to race in IMSA races in the USA. When GT racing revived after the collapse of the world sports car championship in the 1990s, the lead in defining rules was taken by the ACO. Under the ACO rules, Grand Touring cars are divided into two categories, Grand Touring 1 (GT1, formerly GTS) and Grand Touring 2 (GT2, formerly GT). As the name of the class implies, the exterior of the car closely resembles that of the production version, while the internal fittings may differ greatly. GT2 cars are very similar to the FIA GT2 classification, and are 'pure' GT cars; that is production exotic cars with relatively few internal modifications for racing. The Porsche 911 is currently the most popular car in the GT2 class.

FIA divides GT cars into four categories called GT1 (formerly GT), GT2 (formerly N-GT), GT3 (recently introduced) and GT4. The GT1 and GT2 divisions are very close to the ACO rules outlined above, and again some crossover racing does occur, particularly in the GT2 class. The GT3 class is new and was introduced for 2006. These cars are closer to standard form than in GT2, and in most cases modifications are restricted to those found in one-make cups. GT4 is another new category for non-professional drivers in production-based cars with very few racing modifications - for example, no aerodynamic aids or body modifications are permitted.Grand-Am has only one class for Grand Touring cars, allowing production-based cars somewhere around FIA GT3 in terms of modification, with less-powerful Porsche 911 GT3 Cup cars allowed.