This unique book offers a comprehensive guide to the fascinating world of polystomatid flatworms. It introduces the reader to the individual life histories of polystomes and the chronological advances in our knowledge, with descriptions of species discovered over the past centuries. It equips newcomers to the field with basic protocols and techniques for collecting, processing and interpreting material. It also presents the history of research on this group of parasites, provides information on the discovery of each polystome and acknowledges the authors that have made major contributions. For the established researcher in the field, it offers a reference book containing taxonomic data, measurements and drawings of all known polystomes. The authors have brought together all the available material, creating a resource that will stimulate research and revive the global focus on this unique group of parasites. Thus, this work provides an essential reference for both established researchers and newcomers to the field.