Numerous errors and confusion in the literature concerning the genus Trichogramma in Japan have necessitated a formal review of this genus. This review corrects and updates Trichogramma host and distribution records from Hokkaido to the Ryukyu Islands, redescribes and designates a lectotype for T. jezoense Ishii, records two Trichogramma species new to Japan (T. ostriniae Pang and Chen and T. lingulatum Pang and Chen) and describes three new species (T. yabui Honda and Taylor, T. okinawae Honda, and T. aomoriense Honda). Additionally a key to the species is provided for the 14 known Japanese species as are ITS-2 DNA sequences and SEM micrographs of male genital capsules for the majority of the species to aid biocontrol workers in Trichogramma identification.