The genus Progomphus Selys is revised and the nomenclatural difficulties around the Progomphus versus Gomphoides problem are ironed out. Muttkowski’s name Negomphoides is discarded in favour of Gomphoides Selys, 1854. A key to the 52 species known in the adult stage is constructed, including 20 that are introduced as new, viz. Progomphus virginiae (Brazil), adaptatus (Brazil), elegans (Brazil), australis (Argentina), aberrans (Argentina, Brazil, Paraguay), delicatus (Peru), amazonicus (Brazil), tibialis (Surinam), mexicanus (Mexico, Costa Rica), nervis (Peru), formalis (Ecuador, Peru), boliviensis (Bolivia), anomalus (Ecuador, Panama, Peru), abbreviatus (Colombia), incurvatus (Peru), tantillus (Bolivia), superbus (Ecuador, Venezuela), fassli (Brazil), montanus (Bolivia), and kimminsi (Argentina). Descriptive notes on most of the previously described species are offered and important details are elucidated with camera lucida drawings. Illustrations of P. polygonus are published for the first time. The male accessory genitalia of Ris’ species are described and figured. The type species of the genus, Progomphus gracilis, is redescribed and more fully characterized. A conspectus of the type status and locations is compiled. For 31 of the previously known 33 nominal species type specimens could be located. The type of Progomphus herrerae is apparently lost, while the location of that of Progomphus intricatus is doubtful. Nine lectotypes have been selected. A table summarizing the geographic ranges of single species, and distributional maps of some species groups are added.