The Fourth International Symposium on Turbulent Shear Flows took place at Karlsruhe University in Germany. The papers presented at this Symposium encompassed a similar range to that of the previous meetings, with greater emphasis placed on experimental work, and continued a trend towards the examination of complex flows. Once again, three­ dimensional, recirculating and reacting flows featured strongly in the programme and were complemented by consideration of two-phase flows and discussions of both numerical and experimental techniques. The Symposium brought together some 300 participants from all over the world, and it was evident that there is a need for Turbulent Shear Flows Symposia, in order to obtain and communicate new information useful to researchers in the field of turbulent flows and of interest to engineers who design flow equipment. This volume contains 27 papers selected from more than 100 presentations at the Symposium which have been reviewed and edited before publication. Together they provide an indication of the status of current knowledge on the subjects represented at the Sympo­ sium. They are grouped into four sections, namely: • Fundamentals • Free Flows • Boundary Layers • Reacting Flows As in previous volumes in this series, each section begins with an introductory article con­ sidering the papers which follow in the broader context of available literature and current research.