The question of how eusociality evolved in various insect groups has been a matter of intense debate since the time of Darwin. Little attention, however, has been given to the implications of when eusociality may have arisen. Fossil evidence indicates that eusociality evolved in most major eusocial insect taxa (ants, termites, vespid wasps, corbiculate bees) by the late Cretaceous (>65 million years ago) and probably much earlier. Several lineages of halictid bees (Apiformes: Halictidae) also display various forms of eusociality. Our study uses robust phylogenetic data from three protein-coding nuclear genes ( opsin, wingless, EF-1a) and new dating techniques which incorporate fossil and molecular information to estimate the origins of eusociality in this group. Results indicate that eusociality arose ~25 million years ago independently in each of the three eusocial halictid taxa, revealing what appears to be the most recent eusocial origins within any major insect lineage. These age estimates vary only slightly under different methods and assumptions. These recent origins may explain the high levels of intra- and interspecific social variation observed within these bees, and suggest that halictids may provide a unique window into the evolutionary origins and ecological maintenance of sociality. The timing of eusocial origins in halictids correlates with a period of pronounced climatic warming, which we speculate may have been a decisive factor causing the evolution of eusociality in this group.