The IMACS-COST conference on "Computational Fluid Dynamics, Three-Dimensional Complex Flows" was held in Lausanne, Switzerland, September 13 - 15, 1995. The scien tific sponsors of the conference were • IMACS: International Association for Mathematics and Computers in Simulation, • COST: European Cooperation in the field of Scientific and Technical Research, • ERCOFTAC: European Research Community on Flow, Turbulence and Combus tion. The scientific interests of the IMACS and ERCOFTAC associations are closely related to computational fluid dynamics whereas the European Union programme COST covers a wider range of scientific subjects. The COST' Action F1' launched in 1992 by Professor I. L. Ryhming deals with "Complex three-dimensional viscous flows: prediction, modelling, manipulation and control". It has several subtopics among which numerical methods and modelling issues are the main areas of research and development. The meeting gathered together eighty-seven scientists, engineers and researchers from sev enteen countries: Belgium, Finland, France, Germany, Greece, Hong Kong, Israel, Italy, Japan, the Netherlands, Norway, Russia, Spain, Sweden, Switzerland, United Kingdom, United States of America. All major numerical approximation methods were discussed: finite differences, finite volumes, finite elements, spectral methods. The topics covered by the sixty communications spanned the full spectrum of computational fluid dynam ics: direct numerical simulation, large-eddy simulation, turbulence modelling, free surface flows, non Newtonian fluids, thermal convection, etc.