When the race launched in 1923, the competing vehicles were the cars manufacturers sold to the general public, categorised broadly as Sports Cars in contrast to the purpose-built machinery of Grand Prix racing. The underlying philosophy was to test not outright speed but the ability of manufacturers to produce sporty yet reliable vehicles — a concept that encouraged innovation in fuel efficiency and mechanical endurance rather than raw performance.
Over the following decades the cars progressively diverged from their road-car origins. Organisers periodically restructured categories to reflect this reality and to manage performance gaps between machinery.
The oil crisis of the early 1970s prompted the ACO to adopt a fuel economy formula later formalised as Group C, which limited the amount of fuel each car was permitted to use. The regulation shaped the design of prototype machinery across the 1980s and into the early 1990s and is credited with driving innovation in efficient combustion that subsequently found its way into road car engineering.
By the 2000s the class structure had settled into a two-tier framework: Le Mans Prototypes (LMP) at the top, contested by purpose-built machinery unconstrained by road-car requirements, and Grand Touring (GT) cars at the lower tier, based on production models. The LMP tier was itself split into LMP1 — the open-class top division — and LMP2, where teams were required to use approved customer chassis.
In the LMP1 class during the 2000s and 2010s, manufacturers including Audi, Peugeot, Toyota, Porsche, and Nissan fielded factory-backed prototype programmes. Audi won multiple times with turbodiesel machinery beginning with the R10 TDI in 2006, and Porsche — the most successful manufacturer in Le Mans history with nineteen overall victories — returned in 2014 with a hybrid LMP1 programme and won in 2015, 2016, and 2017 with the 919 Hybrid. In the GT classes, the Corvette Racing Team scored multiple class victories in the GTS category in 2001, 2002, and 2004.
In the LMP2 category, regulations since introduced oblige all teams to use one of four approved chassis — ORECA, Ligier, Dallara, or Multimatic/Riley — fitted with a standardised 4.2-litre Gibson V8 engine, with ORECA being the most commonly used.
From 2021, the LMP1 class was succeeded by the Hypercar class (designated LMH or LMDh). The new regulations were designed to prevent the runaway cost escalations that had characterised the late LMP1 era, while enabling greater variety in technical approaches and car aesthetics. As of 2021, the race comprises three classes: Hypercar, LMP2, and LMGT3 (the latter replacing the former LMGTE category in 2024).
A separate non-competitive classification, Garage 56, allows concept cars testing new automotive technologies to participate in the race without being expected to challenge for class honours. The programme debuted in 2012.
All cars compete at the same time regardless of class, with a prize awarded to the winner of each class and to the overall finisher. To be classified, a car must complete the final lap of the race and must have covered at least seventy percent of the distance completed by the overall winner. Failure to meet the seventy-percent threshold — through poor reliability or pace — excludes a car from the results even if it finishes the last lap.