The market share of Diesel engine passenger cars has increased during the last years in Europe and will become a factor of significance also in Asia and in the USA in the near future. This is mainly due to the outstanding good fuel economy of Diesel engines compared to gasoline engines. Namely the recent development and the introduction of the DI-Diesel technology also for passenger car size engines provided a major contribution in the reduction of the passenger car fuel consumption.State of the art passenger car Diesel engines have overcome the drawbacks of the Diesel engine in terms of poor driveability, low specific power output and annoying noise behaviour compared the gasoline engines since turbocharging and intercooling are available for mass production passenger car engines and very efficiently combustion process and structure optimizations have been carried out.Further development efforts have been undertaken to comply with the stringent emission regulations of the future. Such measures are besides the turbocharging and intercooling, the introduction of the four valve technology, high pressure Diesel injection, electronically controlled injection systems and further increased boosting pressure of the engines.In this paper, the boundary conditions for the development of modern passenger car Diesel engines are outlined. The relevant design and combustion parameters as well as a comparison between existing gasoline engines and Diesel engines will be addressed.