AbstractThe morphology, biology and life history of the immature stages, the free‐living and the neotenic females (of the suborders Mengenillidia and Stylopidia respectively) and the free‐living males of the order Strepsiptera are discussed. Strepsiptera are entomophagous parasitoids and are known to parasitize seven orders and thirty‐five families of Insecta. The morphological and physiological changes they cause to the host insect are outlined. The classification of the order is revised; the geographical distribution, phylogenetic system and keys to the families, subfamilies and genera (when possible) are given. As the sexes are dimorphic, separate keys are provided for adult males and neotenic fe