Objectives of the paper are to provide dichotomous keys for the identification of ophidiiform genera. For each genus a brief account is presented including synonymy, a short diagnosis, a list of species, distribution, references, when possible comments on relationships, and for most an outline drawing. The genera are organized into an hierarchical classification which divides them into two suborders, Ophidioidei, which contains oviparous fishes with a high anterior nostril, and Bythitoidei which contains viviparous fishes with a low anterior nostril. Ophidioidei is divided into two families. Carapidae, with a vexillifer larval stage, has two subfamilies: Pyramodontinae with two genera and Carapinae with four. Ophidiidae has four subfamilies: Brotulinae, with a single genus; Brotulotaeniinae (new family) with a single genus; Ophidiinae, the cusk eels, with eight genera in two tribes; and Neobythitinae, with 38 genera (Epetriodus and Spottobrotula are new genera based on new species from the Indian Ocean) in two tribes. Bythitoidei contains two families, one of which, Aphyonidae has five genera characterized by many neotenic features. Bythitidae is divided into the free-tailed Brosmophycinae with 13 genera in two tribes and Bythitinae with 15 genera.