In vitro production of parasitoids has been developed especially for some species of that are being successfully used in biological control programs. The in vitro rearing technology has been intensively studied for a minute egg parasitoid, Trichogramma, because it has shown to be one of the most used natural enemies around the world. This special attention is close related to the economical interest in mass producing and commercializing natural enemies, since they may be inundatively released. Despite the great economical appeal involving this area, few species were successfully reared using this technology. We are going to review the research on this area and discuss some points that limit the development of an in vitro rearing technology, especially the lack of basic research on the functional morphology of the immature parasitoid, host feeding behavior, inter- and infra-specific interactions, and host selection. We also discuss the benefits of the in vitro rearing of parasitoids on the development of basic research on other areas as well as on the genetic manipulation of these insects.