A new classification for the genus groups of Diplogastridae sensu lato is suggested based on a previously published cladogram. The parasitic taxa are included. Only 28 of the published 83 genus names are accepted. For eighteen of these taxa, monophyly is supported by apomorphies, whereas possible paraphyly could not be ruled out for five genera. Five taxa are monotypic. The central part of this paper is a catalogue: a list of genus group names and their synonyms and a list of all species, with information on their habitats. Some 312 species could be placed in these generic groups, whereas five described species are designated as species incertae sedis of Diplogastridae. Subspecies were distinguished in four species. Several species names are removed from synonymy, and new combinations are proposed for 77 species names. Twenty-three new synonyms are suggested for genus groups and eight for species names. A total of 58 species names is regarded as junior synonyms. One new name is proposed: Acrostichus lazarevskajae nom. nov. for A. minimus. Isakis is a nomen oblitum, senior synonym of Pristionchus (nomen protectum). The epitheta of 383 available names are listed in alphabetical order to give an overview of all published species and subspecies names of Diplogastridae, including four names of outgroup taxa that were originally published in combination with a genus of Diplogastridae. A list of nomina nuda is also given, comprising nine species names and three genus group names. We present the reconstructed stem species pattern for Diplogastridae in words and figures as well as synoptic picture tables and diagnoses for the identification of the different generic groups. The genera Aenigmenchus, Noteodiplogaster and Patanodontus are excluded from the Diplogastridae; Patanodontus is a new synonym of Steinernema. Two species are transferred to Steinernema: S. acaudatum and S. octodontum. Diplogaster parasitica belongs to Rhabditidae.