This second edition incorporates development and changes in the taxonomy of Tylenchida since 1986. The book is divided into 9 chapters - I. Introduction, Historical Review and Techniques; II. Morphological characters and taxonomic methods; III. Order Tylenchida; IV. Suborder Tylenchina; V. Infraorder Anguinata; VI. Suborder Hoplolaimina; VII. Superfamily Dolichodoroidea; VIII. Suborder Criconematina; IX. Suborder Hexatylina. There are 1163 references listed at the back, as is an index to all the taxa-subgenera and all higher taxonomic categories of Tylenchida that have been diagnosed and discussed in the book. In this edition, the classification is upgraded and several changes made including the recognition of Hoplolaimina, removal of Myenchina from Tylenchida and the proposals of Anguinata and Tylenchata as infraorders of Tylenchina. Hoplolaimina, recognised by the presence of phasmids and didelphy, has two superfamilies - Hoplolaimoidea and Dolichodoroidea. Hoplolaimoidea has five families - Hoplolaimidae, Rotylenchulidae, Pratylenchidae, Meloidogynidae and Heteroderidae. The revised system of classification and composition of Tylenchida are compared with those of Maggenti et al. (1988). Taxonomic comments are frequently made on the changes proposed in the book. Brachydorinae subfam. nov. is proposed for Brachydorus under Dolichodoridae and Tanzaniinae subfam. nov. is proposed under Tylenchidae. Merodorinae is assigned to Telotylenchidae. Heteroderidae contains Heteroderinae, Meloidoderinae and Ataloderinae. Basirienchus and Rhabdotylenchus have been synonymised with Basiria, and Brevicephalodera with Afenestrata. New genera proposed are: Fraglenchus in Tylenchinae, Telomalenchus as a new subgenus of Malenchus and Ridgellus in Duosulciinae, Chilenchus under Ecphyadophoroidinae, Ethiolaimus as a subgenus of Hoplolaimus in Hoplolaiminae, and Orphreyus as a subgenus of Ogma in Criconematinae. Calvatylus, Pararotylenchus and Plesiorotylenchus have been considered as subgenera of Rotylenchus and Amphisbaenema and Macrocriconema as subgenera of Criconema and Ogma, respectively. Macroposthonia is considered as a valid genus and Criconemella as a subgenus of Criconemoides. Skarbilovinema, Wachekitylenchus and Incurvinema have been assigned to Iotonchinae, Kurochkinitylenchinae and Spilotylenchinae, respectively, and Rubzovinema to Rubzovinematinae of Neotylenchidae. All the species proposed under the order Tylenchida are listed under their respective genera. Full generic diagnosis and differential keys are provided for all 225 valid genera of Tylenchida, 21 of these are considered as subgenera, 3 as genera dubia and another 3 as genera inquirenda. There are 105 genera listed as invalid synonyms. The number of species considered as valid in Tylenchida is 2828; in addition 413 species have been regarded as invalid synonyms while 163 species are considered as species inquirendae/dubiae requiring further study. Neodolichodorus rageshi sp. nov. is proposed for Neodolichodorus sp. apud Rashid, Geraert & Sharma, 1987. There are 101 new combinations proposed.