A major area of investigation in evolutionary biology is the evolution of complex traits. The number of states, the order in which they arise, and the number of times a trait has evolved interest evolutionary biologists. Such studies are only made possible by reconstructing phylogenies in the context of the taxa. Biological investigations rely on accurate species designations and delimitations, and lack of well-defined taxonomic groups impedes scientific progress. Pompilidae (Insecta: Hymenoptera), popularly known as spider wasps, are predatory insects that provision their offspring with spiders as the sole food source. Adult female wasps attack spiders and paralyze them with venom, then place them in simple nests that are usually dug in the soil. Spider wasps form a large and cosmopolitan family with nearly 5,000 described species. Although all Pompilidae have similar biology, there is considerable variation in the nest construction and provisioning behavior; thus, this family could be useful for understanding the evolution of complex behavior. My study aims to evaluate and solve several taxonomic conflicts in spider wasps by reconstructing the complex evolution of behavioral patterns using a molecular phylogenetic framework. Early stages of sociality are found in spider wasps, such as communalism (females of same generation nesting together). My ultimate goal was to study the evolution of communalism in these wasps. I reconstructed relationships at the subfamily and tribal levels for the family, as well as generic and specific levels for pre-defined lineages using five nuclear markers (28S, EF, Pol2, LWRh, Wg), one mitochondrial marker (COI), and morphological characters. These studies comprise the first attempt to revise generic, tribal, and species delimitations for spider wasps, based on robust molecular evolutionary trees. Finally, by studying early stages of social evolution, my results will provide for a better understanding the evolution of social behavior in Hymenoptera as a whole.