This final volume in the treatise Keys to Parastic Nematodes is devoted to the characters of five suborders of nematodes, compiled by five specialists. Suborder Trichocephalata and Diotophymata were compiled by K.I. Skryabin and N.P. Shikhobalova, and Rhabditata and Tylenchata by A.A. Sobolev and A.A. Paramonov. A.A. Sobolev analyzed the material on Camallanta, while V.E. Sudarikov compiled the chapter on the distribution of all known nematodes in different hosts recorded thus far, for all four volumes of this key. The importance of this volume is enhanced further by the most comprehensive index of animal hosts of all known parasitic nematodes reviewed. This comprehensive work is the first of its kind in helminthological literature; this type of treatise has never before been published in any country to date.