Examples from Connecticut apple, Malus domestica Borkhausen, orchards and from the literature are used to review the biology and impact of parasitoids of Phyllonorycter spp. in northeastern North American orchards. These leafminers are parasitized by at least 28 hymenopteran species, which differ in abundance within and between generations and between sites. Typically, higher rates of parasitism and greater species diversity occur in unsprayed than sprayed orchards. The braconid, Pholetesor ornigis (Weed), reaches its highest abundance in orchards infested by the spotted tentiform leafminer. Phyllonorycter blancardella (F.). The eulophid, Sympiesis marylandensis Girault, is dominant in orchards infested by the apple blotch leafminer. Phyllonorycter crataegella (Clemens). The two major native parasitoids, P. ornigis and S. marylandensis, differ in many of their biological attributes, including host synchronization and reproductive potential, and presumably in their effectiveness as biological control agents. The eulophid congregates near the orchard periphery, which is closest to its wild reservoirs in adjacent forest. This parasitoid will be affected negatively by the integrated pest management tactic of spraying of border rows of trees to control immigrating insects unless it develops resistance or unless chemicals less toxic to it are used. In orchards of the future, insecticide applications probably will be fewer in number or more selective in their target. Thus, the amount of parasitism should increase to levels above those now observed. Opportunities may then exist to establish exotic parasitoids to enhance biocontrol of leafminers. More research in lightly-sprayed orchards may offer insights about the future impact of parasitoids and the pest status of leafminers. Such information, coupled with studies of the behavioral ecology of parasitoids, should aid in integrating biological control of leafminers into future programs for apple pest management.