The genus Histeromerus Wesmael, 1838 (Braconidae: Histeromerinae) is revised and its species are keyed. The type species is redescribed and fully illustrated. The genus Mithotynia Hedqvist, 1976, is a new junior synonym of Histeromerus, and its type species, M. aptera Hedqvist, 1976, a junior synonym of H. mystacinus Wesmael, 1838. Histeromerus canadensis Ashmead, 1891, is for the first time reported from the Palaearctic region. A lectotype is designated for H. mystacinus Wesmael, 1838.