Control of the alfalfa blotch leafminer,Agromyza frontella(Rondani), in the United States by exotic parasites is an example of classical biological control. This project was analyzed to identify research principles for future projects. Key events that influenced research were 1) identification of the pest; 2) establishment of a specific project without other research objectives; 3) development of recovery techniques; 4) determination that an empty ecological niche existed in the invaded region; and 5) parasite release procedures. Of 14 species introduced, 3 were established:Dacnusa dryas(Nixon) (Braconidae),Chrysocharis punctifaciesDelucchi (Eulophidae), andMiscogaster hortensisWalker (Pteromalidae). The effective braconid and eulophid species were r-strategists with some K-oriented characteristics, were multivoltine, utilized alternate hosts, occupied a previously vacant niche in the invaded area, were intrinsically superior competitors and long lived, had high searching capacities, and were from many localities in Europe. Benefit in 1983 was 13 million; research cost was ca. 1 million. Research approaches, parasite selection, life table studies, and role of alternative hosts are considered.