This volume includes versions of papers selected from those presented at the THIESEL 2000 Conference on Thermofluidynamic Processes in Diesel Engines, held at the Universidad Politecnica de Valencia, during the period of September th th 13 to 15 , 2000. The papers are grouped into seven thematic areas: State of the Art and Prospective, Fuels for Diesel Engines, Injection System and Spray Formation, Combustion and Pollutant Formation, Modelling, Experimental Techniques, and Air Management. These areas cover most of the technologies and research strategies that may allow Light Duty and Heavy Duty Diesel engines to comply with current and forthcoming emission standards, while maintaining or improving fuel consumption. The main objectives of the conference were to bring together ideas and experience from Industry and Universities to facilitate interchange of information and to promote discussion of future research and development needs. The technical papers emphasised the use diagnostic and simulation techniques and their relationship to engineering practice and the advancement of the Diesel engine. We hope that this approach, which proved to be successful at the Conference, is reflected in this volume. We thank all those who contributed to the success of the Conference, and particularly the members of the Advisory Committee who assessed abstracts and chaired many of the technical sessions. Weare also grateful to participants who presented their work or contributed to the many discussions. Finally, the Conference benefitted from financial support from the organisations listed below and we are glad to have this opportunity to record our gratitude.