Abstract
Chalcidoidea have a long history that dates back to mentions by Aristotle, but with the first chalcids described as other hymenopterans by Linnaeus. As species were correctly placed in later treatments, their early family classifications were diverse, even until very recently. This chapter summarizes the long and varied classification history of Chalcidoidea, along with a review of the various morphological and molecular hypotheses of phylogenetic relationships. The monophyly of Chalcidoidea has only rarely been questioned, but the relationships and inclusion of taxa in various family groups has been far more controversial. The recent results of phylogenomic analyses have resulted in a new recognition of 50 extant families. Another three extinct families are now recognized based on their distinctive morphologies.