This checklist of the Lepidoptera (butterflies and moths) of Alberta lists 2367 species reported to occur in the province, as well as 138 species whose occurrence in Alberta is probable. Each species entry includes adult flight time and distribution status in the Cordilleran, Boreal, and Grasslands ecozones, as well as references to taxonomic works and to the literature and public collection sources of the records. Detailed notes on taxonomy, nomenclature, distribution, habitat, and biology are given for 1524 of the listed species. An additional section provides details on 171 species erroneously reported from Alberta in previous works. The authors hope it will be a useful resource for anyone carrying out species-level work on Lepidoptera in western Canada, or taxonomic work on Lepidoptera in general. An introductory section provides a general overview of the order Lepidoptera and the natural regions of Alberta, and the history and current state of knowledge of Alberta Lepidoptera. Each of the 63 families (and selected subfamilies) occurring in Alberta is briefly reviewed, with information on distinguishing features, general appearance, and general biology. The list is accompanied by an appendix of proposed nomenclature changes, consisting of revised status for 25 taxa raised from synonymy to species level, and new synonymy for 20 species-level and one genus-level taxa here considered to be subjective synonyms, with resultant revised synonymy for one taxon and formalization of seven new combinations.