Here we present a phylogeny of beetles ( I nsecta: C oleoptera) based on DNA sequence data from eight nuclear genes, including six single‐copy nuclear protein‐coding genes, for 367 species representing 172 of 183 extant families. Our results refine existing knowledge of relationships among major groups of beetles. Strepsiptera was confirmed as sister to C oleoptera and each of the suborders of C oleoptera was recovered as monophyletic. Interrelationships among the suborders, namely P olyphaga ( A dephaga ( A rchostemata, M yxophaga)), in our study differ from previous studies. Adephaga comprised two clades corresponding to H ydradephaga and G eadephaga. The series and superfamilies of P olyphaga were mostly monophyletic. The traditional C ucujoidea were recovered in three distantly related clades. Lymexyloidea was recovered within T enebrionoidea. Several of the series and superfamilies of P olyphaga received moderate to maximal clade support in most analyses, for example B uprestoidea, C hrysomeloidea, C occinelloidea, C ucujiformia, C urculionoidea, D ascilloidea, E lateroidea, H isteroidea and H ydrophiloidea. However, many of the relationships within P olyphaga lacked compatible resolution under maximum‐likelihood and B ayesian inference, and/or lacked consistently strong nodal support. Overall, we recovered slightly younger estimated divergence times than previous studies for most groups of beetles. The ordinal split between C oleoptera and S trepsiptera was estimated to have occurred in the E arly P ermian. Crown C oleoptera appeared in the Late P ermian, and only one or two lineages survived the end‐ P ermian mass extinction, with stem group representatives of all four suborders appearing by the end of the T riassic. The basal split in P olyphaga was estimated to have occurred in the T riassic, with the stem groups of most series and superfamilies originating during the T riassic or J urassic. Most extant families of beetles were estimated to have C retaceous origins. Overall, C oleoptera experienced an increase in diversification rate compared to the rest of N europteroidea. Furthermore, 10 family‐level clades, all in suborder P olyphaga, were identified as having experienced significant increases in diversification rate. These include most beetle species with phytophagous habits, but also several groups not typically or primarily associated with plants. Most of these groups originated in the C retaceous, which is also when a majority of the most species‐rich beetle families first appeared. An additional 12 clades showed evidence for significant decreases in diversification rate. These clades are species‐poor in the M odern fauna, but collectively exhibit diverse trophic habits. The apparent success of beetles, as measured by species numbers, may result from their associations with widespread and diverse substrates – especially plants, but also including fungi, wood and leaf litter – but what facilitated these associations in the first place or has allowed these associations to flourish likely varies within and between lineages. Our results provide a uniquely well‐resolved temporal and phylogenetic framework for studying patterns of innovation and diversification in C oleoptera, and a foundation for further sampling and resolution of the beetle tree of life.