Because of its outstanding fuel economy and its somewhat lower maintenance costs, the diesel engine has become dominant in the transportation field, especially for heavy-duty trucks. There is evidence that use of diesel engines in medium- and light-duty trucks as well as in passenger cars will increase in the future. Most diesel engines are installed in commercial vehicles. However if the engine is not carefully matched to the transmission and accessories, as well as to the specific vehicle application (severity of duty), the total package may be commercially unattractive.The purpose of this paper is to detail the most important considerations in matching diesel engines with transmission, components, etc., for use in commercial vehicles, specifically truck application. The paper surveys the market currently served by diesel engines, gives an overall view of the engine application process, discusses engine-transmission-vehicle matching and performance, and details the engine services supplied by the vehicle, such as the provision of cool and clean air, water, oil, and fuel, exhaust removal, engine mounting, temperature control of the engine, coolant flow arrangements, accessories, and cold weather operation. Noise and exhaust emissions are also discussed.