This volume is part 8 of a series of monographs on the ichneumon flies of America north of Mexico. The Subfamily Cremastinae is world-wide in distribution, occurring most abundantly in temperate regions, frequently in more arid regions, and less often in colder climates. Hosts are usually lepidopterous and occasionally coleopterous larvae, mostly leaf-rollers, gall-makers, wood-borers, or larvae that tend to hide in buds and similar protective structures. The Cremastinae is an important group in biological control. The subfamily consists of 23 genera, of which 12 are represented in the Nearctic Region. At present approximately 534 species have been described with 322 of these represented in the Nearctic Region.