The book is the first part of the three-volume fundamental monographic treatment of the class Trematoda aimed to be a comprehensive single source allowing the identification of any representative of this largest group of parasitic flatworms to the generic level. It should be mentioned that the class Trematoda, comprising up to 20,000 described species, is the largest group of parasitic Platyhelminthes and probably the largest group of metazoan parasites of animals on the planet. Trematodes, the overwhelming majority of which belong to subclass Digenea, are distributed globally and are found as adults in all groups of vertebrates. At the same time, they utilize as intermediate and paratenic hosts in their life cycles many groups of molluscs, arthropods and some vertebrates. Taking into account the huge number of genera and families as well as the vast number of original publications devoted to these parasites, their identification has never been an easy task even for experts. Until recently, only two major works have been published that targeted all digenean taxa. These are the multi-volume series of "Trematodes of Animals and Man. Essentials of Trematodology " edited and partly written by K.I. Skryabin, and S. Yamaguti's monograph of 1958 and its major update in 1971. However, both of the above works are now rarities and relatively few new researchers have access to them. Preparation of the "Essentials of Trematodology" series was an immense effort of many authors; however, its publication stretched out over a period of almost 30 years (1947-1974) and thus, the information included in the first volumes, is very outdated. Besides, many of these books have never been translated into English. Although they contained descriptions of almost all species known at the time of publication, in most cases they lacked keys. The "Synopsis of Digenetic Trematodes" (1971) by S. Yamaguti was and is, a unique reference book that provided keys to genera and listings of species known at the time. These books served parasitologists as an ultimate source of information during almost half a century. More than 30 years passed, however, since the publication of "Synopsis of Digenetic Trematodes" and in some groups, for instance, hemiuroids, a large number of new taxa have been described accompanied by substantial changes in the systematics. Thus, the "Keys to the Trematoda" appeared as a timely response to the obvious need for an updated reference book that would allow everybody dealing with these parasites, to identify them. It is a result of an impressive international effort involving the world's leading experts on trematode systematics. The book is edited by David I. Gibson, Arlene Jones and Rodney A. Bray, the same team of experts who previously edited the excellent "Keys to the Cestode Parasites of Vertebrates " (1994) which proved to be an invaluable identification and systematic resource for specialists working in different fields of parasitology. The editors undoubtedly had a difficult task finding specialists to cover all groups of trematodes due to the steady decrease in number of taxonomists working on digenean systematics. As a result, there are no "narrow" specialists on some particular families of trematodes and, therefore, some of the authors undertook the extremely difficult job of tackling taxa with which they had relatively little experience. And they fulfilled this task remarkably well. The first volume has been prepared by 16 experts from UK, USA, Bulgaria, Poland, Australia and Czech Republic. It includes subclass Aspidogastrea comprising 4 families, and the digenean order Strigeida comprising 11 superfamilies and more than 50 families. The authors of the chapters are: Subclass Aspidogastrea (K. Rohde), superfamilies Azygioidea (D.I. Gibson), Bivesiculoidea (T.H. Cribb), Brachylaimoidea (T. Pojmanska and family Moreauiidae by K. Niewiadomska), Bucephaloidea (R.M. Overstreet and S.S. Curran), Clinostomoidea (family Clinostomidae by I. Kanev, V. Radev and B. Fried, and Liolopidae by K. Niewiadomska), Cyclocoeloidea (I. Kanev, V. Radev and B. Fried), Diplostomoidea (K. Niewiadomska), Gymnophalloidea (Gymnophallidae by T. Scholz and 5 families by R.A. Bray), Hemiuroidea (D.I. Gibson - 12 families in this superfamily alone!), Schistosomatoidea (Schistosomatoidae by L.F. Khalil, Sanguinicolidae by J.W. Smith and Spirorchiidae by T.K. Platt), Transversotrematoidea (T.H. Cribb). Three of the authors deserve particular credit for preparing a lion's share of families - David I. Gibson (13 families and several general chapters), Katarzyna Niewiadomska (9 families) and Teresa Pojmanska (7 families). In my personal opinion, preparation of such a book by a team of authors versus a single author is an advantage because one person, despite all efforts, cannot possess equally good expertise in so many groups of trematodes. In part due to the above reason, the "Keys to the Trematoda" is characterized by a higher proportion of new original drawings, resulting from re-examination of specimens including types. The taxa in the book are arranged according to the systematics of trematodes, not by host groups as was the "Synopsis of Digenetic Trematodes". This design seems to me more logical and more convenient to use because representatives of many digenean supraspecific taxa and sometimes even the same species can be found in more than one class of vertebrates. Each taxon included in the book, is provided with a diagnosis and drawing of at least one representative of each genus. Following the layout of the "Keys to the Cestode Parasites of Vertebrates", the figures in the "Keys to the Trematoda " are conveniently placed within the text, not at the end of the book. I find the overall design of the book very good. The editors did an excellent job minimizing effects of unavoidable writing style differences between different authors. Of course, this could be done to a lesser extent with drawings, which are a very important part of any taxonomic keys. Despite the differences in style, a vast majority of illustrations are of high quality and very helpful in identification. Without implying that other illustrations are any worse, my personal favorites for clarity and level of details are drawings of Bucephaloidea by R.M. Overstreet and S.S. Curran, Gymnophallidae by T. Scholz and Hemiuridae by D.I. Gibson. In contrast, the quality of drawings of the Schistosomatidae seems to me somewhat sub-standard which hopefully does not influence identification. I have only one general remark regarding the layout of the book. Some drawings clearly suffered from too great reduction in size. At the same time, many plates have unoccupied white spaces. Although the high printing quality minimizes this problem, I believe in the next volumes this situation could be improved. Specialists working on particular groups of digeneans may find systematic allocation of some taxa controversial or improper. I find incorrect, for instance, the allocation of the Eucotylidae within the Cyclocoeloidea which does not correspond to available data on their development and morphology, and recent findings in their molecular phylogenetics, which provide evidence that Eucotylidae are closely related to Renicolidae. This is, however, a rather normal situation in the case of such a huge and phylogenetically poorly understood group of organisms as trematodes. They are characterized by innumerable morphological and biological adaptations to their hosts and environment which resulted in a high level of morphological homoplasy. It should be remembered that this book is not a comprehensive systematic/taxonomic revision of the Trematoda, which seems to be an almost unachievable goal at present. The main aim of the book is to provide readers including non-taxonomists, with a tool to identify their specimens of aspidogastreans and digeneans to the generic level. And the book fully achieves this aim. To test the keys, I took almost randomly from my collection a number of digenean specimens from different groups of vertebrates and in almost all cases the keys worked fine given that the specimens were properly fixed adult worms. The editors explicitly described the organization, mode of preparation, scope and main aims of this unique publication. They were fully aware of possible points of weakness deriving from homoplasious nature of some morphological characters of adult digeneans. For instance, in their opinion, the readers should be prepared that the keys to superfamilies may not work reliably in all cases. Some readers may be also somewhat dissatisfied with the level to which systematic revision has been done on certain families. It is true that some groups are practically unchanged while others have been revised in detail. The latter particularly concerns Bucephaloidea by R.M. Overstreet and S.S. Curran, which is supplied by a complete historical and systematic account as well as phylogenetic analysis in the introduction. Of course, readers would be happier to see all groups fully revised. Unfortunately, this aim is not feasible and the editors clearly emphasized in their preface that the priority of these keys is identification. In any case, the book and keys actually provide much more information than one could expect taking into account the magnitude of the goal. For a practical taxonomist, this is one of the books which never make it to the shelf because you shall always want to keep it on your desk at arm's reach. Unlike many other parasitology books dealing with more rapidly developing disciplines like molecular biology or immunology, it is not going to become out-of-date in few years. It will be a major source of information in digenean taxonomy for the next several decades. Moreover, I (unfortunately) have a feeling that a book of this scope and coverage may never be published again due to the almost irreversible and steady process of loss of taxonomic expertise on many groups of parasitic worms including trematodes. Therefore, in my opinion, this is a "must have" book for every institution/laboratory where studies of trematodes are carried out now or anticipated in the future. I would encourage quick acquisition of the book while it is still available because with all certainty, it will rapidly become a rarity after it goes out of print. The book will be useful for taxonomists, medical and veterinary doctors, teachers of parasitology, invertebrate zoology and biodiversity courses, conservation biologists and students aiming at a career in these disciplines.