Aedes communis (Deg.) sens. str. from Canada and the United States, A. nevadensis Chapman and Barr n. status from the northwestern United States, and A. churchillensis sp. n. from western Canada are described. The distribution and keys to the larvae, female imagos, anti male genitalia of the three species are presented. The size and chorionic markings of the eggs of A. communis and A. churchillensis are described and illustrated. Variation in the anatomy and chaetotaxy of the fourth-instar larvae, the anatomy of the salivary glands, and the chaetotaxy of the thorax of female imagos, and the ungues of the imagos is described and illustrated. An autogeny survey revealed that the female imagos oi A. communis and A. nevadensis are normally obligatorily anautogenous or rarely facultatively autogenous whereas those of A. churchillensis are normally obligatorily autogenous. Differences in the size and general anatomy of the salivary glands of A. churchillensis and their possible association with autogeny are discussed. Mating success of caged imagos of A. communis and A. churchillensis, caged separately or together, was evaluated; imagos of the former species are eurygamous whereas those of the latter are stenogamous; some mating between caged imagos of the two species is possible. Observations of mating between imagos of A. communis in nature are discussed in relation to swarming. Hybridization in the laboratory revealed a low degree of genetic affinity between A. communis and A. churchillensis.