This publication deals with the adult mosquitoes of Saskatchewan. Keys to genera and species are given. Six genera are represented in the mosquito fauna, namely: Aedes with 25 species; Culex with three species; Culiseta with five species; Anopheles, Mansonia, Psorophora, and Wyeomyia each with one species. Each species is described and important taxonomic characters are illustrated. Brief notes on biology and distribution follow the description of each species. The topography, climate, and vegetation of the province is discussed in relation to the distribution of mosquitoes. The seasonal distribution of the mosquitoes in the three main ecological zones, namely prairie, aspen grove zone, and coniferous forest zone, is outlined. Brief sections are devoted to mosquito adaptation to survival and to mosquitoes in relation to Western equine encephalomyelitis.