For this sixth volume 01 proceedings stemming lrom a Symposium on the Applications 01 Laser Techniques to Fluid Techniques, we have selected thirty one papers which are presented in live chapters. They represent some 01 the best papers presented at the Sixth Symposium which was again held at the Calouste Gulbenkian Foundation in Lisbon, this time lrom 20 to 23 July 1992. The total number of papers at the Symposium was slightly larger than in 1990 and was selected from a much increased number of abstracts, with a considerably smaller of accepted manuscripts. Thus, this volume represents some 01 the best 01 the best. The topics we have chosen to include are Laser Anemometer Optics and Processing, Two-Phase Flow Instrumentation, Whole-Field Velocimetry, Complex Flow Applications and Engine and Combusting Flows, and they show that there continues to be a healthy interest in the development 01 understanding of the methodology and its implementation in terms 01 new instrumentation, and this is emphasised by the increasing number 01 companies which have attended the Symposium in recent years in order to demonstrate their range 01 products. At the same time, it is clear that there is an increasing range of applications 01 the corresponding laser techniques and this is represented, in part, by the chapters concerned with Complex and Engine and Combusting Flows. In general, we are very pleased with the way the application 01 laser techniques has grown and hope that this se ries 01 Symposia has played its part.