The Audi R18 is a Le Mans Prototype (LMP) racing car constructed by the German car manufacturer Audi AG. It is the successor to the Audi R15 TDI. Like its predecessor, the R18 uses a TDI turbocharged diesel engine but with a reduced capacity of 3.7 litres and in a V6 configuration. For the first time since the 1999 R8C, Audi's Le Mans prototype uses a closed cockpit design. The R18 is also the first racing car from Audi to feature hybrid power.

Although Audi have previously given each new developed model of endurance racing car a distinct model number the head of Audi Sport, Wolfgang Ullrich, suggests the R18 designation for Audi endurance racing cars could be used for the foreseeable future as a result of rival car manufacturer Renault already holding trademarks for car model names R19 through to R35. There have been five further evolutions of R18 since the original spec introduced in 2011, the latest is the 2016 spec which competed in the 2016 World Endurance Championship.

As the new rules for Le Mans in 2011 the car features a stabilisation fin on the engine cover and has a new six-speed gearbox. The new gearbox is electrically controlled instead of pneumatically controlled, saving weight by eliminating the pneumatic system. Despite the capacity reduction, the 3.7L V6 is claimed to develop more than 397 kilowatts (532 bhp) of power. This is less than the outgoing R15, but the V6 engine's fuel consumption will more than likely be lower than that of the outgoing V10 engine on the R15. The new engine has a single Garrett (Honeywell Turbo Technologies) TR30R VGT turbocharger, as opposed to the twin TR30R configuration of both the Peugeot 908 HDi FAP and the previous Audi R15 TDI. The R18's V6 engine exhausts inwards between the cylinder banks, where the turbocharger is placed. This is called a 'hot side inside' configuration and is opposed to the traditional configuration with each cylinder bank of a V engine exhausting outwards to their respective turbochargers.

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