Most top-class sports car races emphasise endurance (generally between 6 and 24 hours), reliability, and strategy, over pure speed.

The prestige of storied marques such as Porsche, Audi,[2] Chevrolet, Ferrari, Jaguar, Bentley, Aston Martin, Lotus, Maserati, Lamborghini, Alfa Romeo, Lancia, Mercedes-Benz, and BMW is built in part upon success in sports car racing.

According to historian Richard Hough, "It is obviously impossible to distinguish between the designers of sports cars and Grand Prix machines during the pre-1914 period.

"[1]In the 1920s, the cars used in endurance racing and Grand Prix were still basically identical, with fenders and two seats, to carry a mechanic if necessary or permitted.

The legendary Alfa Romeo Tipo A Monoposto started the evolution of the true single-seater in the early 1930s; the Grand Prix racer and its miniature voiturette offspring rapidly evolved into high performance single seaters optimised for relatively short races, by dropping fenders and the second seat.

In open-road endurance races across Europe such as the Mille Miglia, Tour de France and Targa Florio, which were often run on dusty roads, the need for fenders and a mechanic or navigator was still there.

As mainly Italian cars and races defined the genre, the category came to be known as Gran Turismo (particularly in the 1950s),[5] as long distances had to be travelled, rather than running around on short circuits only.

After major accidents at the 1955 24 Hours of Le Mans and the 1957 Mille Miglia the power of sports cars was curbed with a 3-litre engine capacity limit applied to them in the World Championship from 1958.

Clubmans provided much entertainment at club-racing level from the 1960s into the 1990s and John Webb revived interest in big sports prototypes with Thundersports in the 1980s.

In Germany, domestic production based racing was largely dominated by BMW, Porsche and Mercedes-Benz, although sports car/GT racing gradually became eclipsed by touring cars and the initially sports car based Deutsche Rennsport Meisterschaft gradually evolved into the Deutsche Tourenwagen Meisterschaft.

Powerful prototypes (effectively pure-bred two-seater racing cars with no real link to production vehicles) started to appear as the 1960s progressed, with worldwide battles between Ferrari, Ford, Porsche, Lotus, Alfa Romeo and Matra as well as other more specialist marques running on into the early 1970s.

Homologation saw many out-and-out racing cars produced in sufficient quantities to see them classed as production vehicles; the FIA responded by placing more restrictions on even the allegedly production-based cars and placed draconian limits on the power available to prototypes – these prototypes of the late 1960s/early 1970s were comfortably quicker than contemporary Grand Prix machinery and for 1972 they were constrained to run much smaller engines to F1 rules, often de-tuned for endurance.

The ACO, organisers of the Le Mans 24 Hours, attempted to come up with a formula that would encourage more prototypes back to the race but would also be relatively economical – their Grand Touring Prototype rules in the late 1970s, based on fuel consumption rules, gave rise to two different varieties of sports car racing that were widely held to be a high point in the history of the sport.

In the US, the IMSA Camel GTP series boasted close competition between huge fields of manufacturer-backed teams and privateer squads – the cars were technically similar to Group Cs but used a sliding scale of weights and engine capacities to try to limit performance.

The FIA attempted to make Group C into a virtual "two seater Grand Prix" format in the early 1990s, with engine rules in common with F1, short race distances, and a schedule dovetailing with that of the F1 rounds.

NASCAR was becoming increasingly dominant, and the IndyCar Series' split from CART in 1996 put more emphasis on ovals regarding domestic open-wheel racing.

This series, known as the SCCA World Challenge, consists of a one-hour race for each round, combining three classes: GT (Chevrolet Corvette, Aston Martin DB9, etc.

The reformatted Trans-Am Series remained stagnant, being heavily overshadowed by the SCCA's World Challenge, and failing to garner a television contract.

Ever since the World Sportscar Championship was conceived, there have been various regulations regarding bodywork, engine style and size, tyres and aerodynamics to which these cars must be built.

Sports prototypes may be (and often are) one-of-a-kind machines, and need bear no relation to any road-going vehicle, although during the 1990s, some manufacturers exploited a loophole in the FIA and ACO rules.

As a result, some cars racing in the GT category did pass as true sports prototypes, in turn leading to some road-going versions for homologation purposes.

In simplistic terms, sports prototypes are two-seat racing cars with bodywork covering their wheels, and are as technically advanced and, depending on the regulations they are built to, as quick as or quicker than their single-seat counterparts.

Although not widely known, sports-prototypes (along with Formula 1 cars) are responsible for introducing the most numbers of new technologies and ideas to motorsport, including rear-wings, ground effect 'venturi' tunnels, fan-assisted aerodynamics and dual-shift gearboxes.

For these reasons, the category being labeled as a "prototype" has occasionally been criticised as misleading and being more in line with traditional "spec" race series prevalent in the United States.

The intention of the DP formula was to provide a class in which tight technical regulations encouraged close competition and where budget would be relatively unimportant.

When GT racing revived after the collapse of the World Sports Car Championship at the end of 1992, the lead in defining rules was taken by the ACO.

The American Le Mans Series also runs a "GT-Challenge" class, which currently only uses Porsche 911 GT3 Cups but will open to other cars next year.

GT1 has been all but phased out with the removal of the class from the FIA GT1 World Championship in favor of GT3 cars, in turn leading to the outright discontinuation of the series.

GT4 has likely been phased out like GT1, with the removal of the category from the Blancpain Endurance Series and the cancellation of the GT4 European Cup for 2012 due to issues regarding the organiser.

Rising costs coupled with declining entries led to the death of this class in 1998, and it was replaced by what was then called GT2 (by the FIA, which later evolved into the GT1) and Le Mans Prototype (LMP, by the ACO).