The worldwide trend to increasingly stringent exhaust emissions standards, together with consumer requirements, are forcing both vehicle and engine manufacturers, as well as manufacturers of ancilliary equipment, to introduce new and often novel technology in order to produce clean, quiet and socially acceptable transport at affordable prices. The combustion process lies at the heart of the engine and the quality of the combustion determines the acceptability of the product to a very large extent. The fuel injection system plays a large role in the combustion process and in consequence, the fuel system type and capabilities strongly influence the performance of the combustion system.There has never been such a range of fuel injection systems available at one time as there is today. High pressure hydraulically actuated systems /1/ compete with cam driven fuel injection systems /2/ to deliver the injection requirements demanded by the vehicles both of today and in the future. The demands placed on the fuel injection system are addressed together with the types of fuel injection systems emerging. All of these systems have strengths and weaknesses relative to one another which will also be discussed. Based upon the results of test work at AVL on all of these various systems, the differences between the systems will be presented and assessed with respect to engine performance, emissions, fuel consumption and noise.In conclusion an outlook is given as to how the various routes are likely to progress and the consequences for the engine and vehicle manufacturer of the different approaches.