The subfamily Microgastrinae is redefined; Cardiochilinae and Miracinae are placed as separate subfamilies. The Microgastrinae are divided into five tribes and 51 genera, 23 of which are new. The first two tribes, Apantelini and Microgastrini, have characteristically long ovipositor and are almost all solitary parasites of Microlepidoptera. The other three tribes, Forniciini, Cotesiini and Microplitini, have short ovipositor and are almost all parasites of Macrolepidoptera, usually gregarious. The genera Pseudapanteles, Parapanteles, Glyptapanteles and Protapanteles of Ashmead, Cotesia Cameron, Dolichogenidea and Diolcogaster Viereck are revived from synonymy, and the following new genera are described: Alphomelon, Choeras, Clarkinella, Deuterixys, Distatrix, Exix, Exoryza, Exulonyx, Iconella, Illidops, Nyereria, Papanteles, Paroplitis, Pelicope, Pholetesor, Rasivalva, Rhygoplitis, Sathon, Teremys, Venanides, Venanus, Wilkinsonellus, Xenogaster. Twenty new species are described and about 350 new combinations are given.