Fuel injection is a fuel system which injects precisely metered amounts of fuel into an intake system (indirect injection) or directly into the cylinder (direct injection).

Injection systems lend themselves to control by computer, which provides far more precise management of fuelling than is possible using a carburettor.

Injection is a necessity for a practical diesel engine, and on these engines injection has been in use since the 1930s. The first road-going fuel injection system for a petrol car was the 1954 Mercedes-Benz 300SL. Mechanical fuel injection systems became popular on premium and performance cars in the 1970s and took over completely in the 1990s thanks to the standardization of catalytic converters.