This book is the first to provide an identification key to this important freshwater group of algae which enables the user to work from live specimens. The use of fresh material means that time-consuming preparation techniques can be avoided enabling analyses to be made within a short time of collection. Also the diatoms can be counted, identified and studied at the same time as other algae in the sample. The book provides a general introduction to the diatoms including a resume of the variety of chloroplast forms encountered, a review of colony types, a guide to shape terminology and also information on how to measure cells. The keys are designed for the specialist and the non-specialist alike, allowing two points of entry and the identification of most common taxa to species level. When cleaned material is necessary for unequivocal identification, this is indicated. The book also contains a list of all species included with brief ecological notes on occurrences and distribution along with a glossary of terms. This book will be of immense use to biologists studying algal communities in freshwater ecosystems and particularly to those involved in monitoring programmes. The increasing realization of the importance of algae to the health of aquatic ecosystems, and the developing use of diatoms as environmental indicators means that this volume will become an invaluable aid to the water industries and environmental protection agencies.