The superfamily Chalcidoidea (the jewel wasps) are part of the insect order Hymenoptera. The superfamily comprises more than 27,000 known species, with an estimated total diversity of more than 500,000 species, meaning that the vast majority have yet to be discovered and described. Most of the species are parasitoids, attacking the egg, larval stage or pupal stage of their host, though many other life cycles are known including gall associates and fig pollinators. This landmark volume has been co-authored by world authorities on the systematics and biology of chalcidoid wasps. It provides an introduction to the superfamily, a review of chalcidoid morphology, an overview of the fossil record, a phylogenetic framework for the revised classification of the superfamily, an identification key for the 50 recognized families, and detailed treatments of the individual families. The book consolidates much recent research on the phylogenomics of Chalcidoidea and the fossil record. This research has resulted in substantial changes to their classification, and in a review of all families, the new family groups are presented to the general scientific public for the first time. The book is an historic milestone, presenting a reclassification of the superfamily and a synthesis of knowledge on all aspects of Chalcidoidea that will serve for generations to come. Individual chapters clarify the limits of families and subfamilies based on contemporary phylogenetic studies. These chapters provide for each family: diagnostic features and extensively illustrated details of their specialized morphology, summaries of their distribution and worldwide diversity, a history of their classification history and major workers, phylogenetic relationships, natural history, use in biological control and economic impact, fossil history, and fully illustrated identification keys to subfamilies or in some cases to genera. Additional chapters present best practices for collecting, rearing from hosts, and preservation, review digital resources currently available, explore the diversity of their natural history and their human impacts, such as their use and importance to biological and natural control of pest arthropods. Chapters by worldwide authorities explore the enormous biological diversity of chalcidoid wasps including consequences of their almost unbelievable miniaturization (the most extreme known in insects), relationships with endosymbionts, special aspects of genetics, genomics, evolutionary biology and development, and brief accounts of the most significant chalcidoid researchers that have passed. For many years to come this important book will serve the needs of hymenopterists and professional entomologists, taxonomists and systematists, entomologists working on parasitic wasps as biological control agents, and ecologists working on parasite-host interactions.