This book is an outcome of the III Workshop on Hydrozoa Biology organized by the Hydrozoan Society and held in the marine station of Roscoff (France) from the 19 of September till the first of October 1994. Through a series of selected papers, this volume covers a wide range of topics comprising traditional systematics, zoogeography, life cycles, ecology, behaviour, evolution as well as some molecular biological approaches. This collection of scientific papers all written by experts in their field make this book a valuable addition to Hydrozoan research. As a whole, they are a good sample of the different research fields now alive and well in marine invertebrate biology. It should find it place in libraries of marine stations and universities.