Ninety-five species of aquatic and semiaquatic Heteroptera are recorded from the Prairie Provinces of Canada, representing the following families: Belostomatidae 3, Corixidae 41, Gelastocoridae 1, Gerridae 8, Hebridae 2, Hydrometridae 1, Mesoveliidae 1, Nepidae 2, Notonectidae 6, Pleidae 1, Saldidae 26, and Veliidae 3. Also included are data on distribution, habits, and biological information. Keys to families, genera, and species are given, with 138 illustrations.