Our understanding of how natural selection and demographic processes produce and maintain biological diversity remains limited. However, developments in high-throughput genomic sequencing coupled with new analytical tools and phylogenetic methods now allow detailed analyses of evolutionary patterns in genes and genomes responding to specific demographic events, ecological changes, or other selection pressures. Here, we propose that the mosquitoes in the Culex pipiens complex, which include taxa of significant medical importance, provide an exceptional system for examining the mechanisms underlying speciation and taxonomic radiation. Furthermore, these insects may shed light on the influences that historical and contemporary admixture have on taxonomic integrity. Such studies will have specific importance for mitigating the disease and nuisance burdens caused by these mosquitoes. More broadly, they could inform predictions about future evolutionary trajectories in response to changing environments and patterns of evolution in other cosmopolitan and invasive species that have developed recent associations with humans.