This third volume of Keys to Parasitic Nematodes is devoted to the largest suborder of nematodes - the strongylates. The strongylates include extremely pathogenic helminths which in a number of cases cause serious disease in man and in farm and commercial animals, often with a fatal outcome. Examples of these are anchylostomiasis and necatoriasis in man, delafondiasis and alfortiasis of horse, hemonchiasis and chabertiasis of sheep and dogs, bunostomiasis of cattle, hyostrongylosis of swine, etc. Due to the pathogenicity of the strongylates, it is natural that veterinarians and physicians, as well as biologists, should wish to familiarize themselves with the classification of these helminths. The present volume is "Key" which constitutes a handbook that includes all strongylates known at present to be animal parasites in all geographical zones of the world. However, this volume is not merely a mechanical list of all species comprising the strongylate group. The authors have carried out a thorough analysis of existing concepts relating to the taxonomy of this group of nematodes and now present a new system of classification of the strongylates based on all the material that was studied. In all, the new system embraced by the authors puts forward three super families, 17 families, 51 subfamilies and 245 genera.