Apidae (Hymenoptera) is the most speciose family of bees with over 5600 species. The family is notable for having some of the most important pollinators of managed crops, yet also comprises a rich diversity of social and parasitic lifestyles, host plant affinities, and ecosystem services. Despite its importance, relationships among the tribes within Apidae remain unclear. To date, rigorous phylogenetic analysis has been challenged by long-standing assumptions about the relatedness of cleptoparasitic groups in relation to their hosts. I performed the first large-scale phylogenetic study of the family Apidae based on DNA sequence data, including representative taxa from all 33 apid tribes. I then used this phylogeny to investigate the origins and antiquity of cleptoparasitism and sociality. Results indicate that most cleptoparasitic apid bees form a monophyletic group, and therefore stem from a single origin of cleptoparasitism (with two more origins in the Euglossini orchid bees and one in the tribe Ctenoplectrini). Divergence time analysis using a relaxed fossilcalibrated molecular clock model reveals that cleptoparasitism is an ancient behavior in apid bees that first evolved ~100 Ma. Results also indicate that primitive eusociality is the ancestral state for corbiculate Apidae, and that orchid bees represent a reversal from eusociality to solitary, communal, and weakly social behavior. According to my divergence time analysis, eusociality first evolved ~87 Ma in the corbiculates, much earlier than in other groups of bees. To date the origin of bees and their major clades, I performed a phylogenetic analysis of bees including representatives from every subfamily, and almost all tribes, using sequence data from seven genes. I then conducted a fossil-calibrated relaxed clock divergence time analysis. I estimate that bees originated at the start of the Aptian, concurrently with the origin of the eudicot angiosperms. All of the major bee clades are estimated to have originated during the middle to late Cretaceous, which is when angiosperms diversified to becom the dominant group of land plants. This study firmly establishes temporal overlap in the diversification of bees and angiosperms, a necessary precondition for the role of bees in the angiosperms’ rise to dominance during the late Cretaceous.