Tachinidae are one of the most diverse and ecologically important families in the order Diptera. As parasitoids, they are important natural enemies in most terrestrial ecological communities, particularly as natural enemies of larval Lepidoptera. Despite their diversity and ecological impact, relatively little is known about the evolution and ecology of tachinids, and what is known tends to be widely dispersed in specialized reports, journals, or texts. In this review we synthesize information on the evolutionary history, behavior, and ecology of tachinids and discuss promising directions for future research involving tachinids. We provide an overview of the phylogenetic history and geographic diversity of tachinids, examine the evolution of oviposition strategies and host associations, review known mechanisms of host location, and discuss recent studies dealing with the ecological interactions between tachinids and their hosts. In doing so, we highlight ways in which investigation of these parasitoids provides insight into such topics as biogeographic patterns of diversity, the evolution of ecological specialization, the tritrophic context of enemy-herbivore interactions, and the role of host location behavior in shaping host range.