Among the egg parasites used extensively for biological control of various lepidopterous pests all over the world the species ofTrichogramma andTrichogrammatoidea (Hymenoptera, Trichogrammatidae) are the most important. The mode of reproduction of most of these is arrhenotoky while a few inTrichogramma is thelytoky, the later could be facultative with change in temperature, from one mode to the other. Since 1977, a large number of new species were described and studies on different aspects made world over. The studies made include crossing experiments which proved existence in nature of sibling species and other categories of incipient speciation which otherwise are difficult to discern. Studies on isozyme and enzyme analyses showed important differences among species and populations ofTrichogramma, so also response by these to different chemical insecticides. Scanning electron microscopy is yet another important tool to supplement other differentiating factors. Other biological characters aiding systematics include sex ratio, life and fertility table studies showing breeding potential, host preferences, temperature tolerance, etc.