The basic forms of in-line and distributor pumps in use on automotive diesel engines are described, as well as some of the types of injector used on direct and indirect injection engines. The paper gives the results of computer calculations illustrating the difference between the rate of pumping and the rate of injection in a pump- pipe-nozzle system and in a unit injector. The paper then describes the influence of rate of injection on engine performance and emissions, and shows how a fuel injection specification can be optimised by the use of tradeoff curves. The main sources of unburnt hydrocarbons are described.As legislative levels of emissions become more severe, more accurate and flexible control of injection is required, and considerable work has been done in recent years on electronic control. The paper describes some electronically controlled fuel injection systems.