This publication presents illustrated keys to the 19 families and 706 described genera of Chalcidoidea known to occur in the Nearctic region (minimally America north of Mexico, but also including those areas of Mexico generally considered as having a Nearctic insect fauna). The first three chapters provide an introduction to this superfamily of wasps, most of whose members are parasites of other insects; a review of chalcidoid morphology as related to terms used in the keys & diagnoses; and an overview of the superfamily, including a 41 couplet key to families. Each of the remaining 19 chapters reviews one family & includes sections on recognition, systematics & relationships, biology, literature, an annotated key to the Nearctic genera, and for larger families an index to genera based on couplet number. Over 1,800 line drawings & electron micrographs illustrate the keys. Annotations include references to existing keys to species, estimated number of species, and known distribution & host range in the region.