This checklist documents the 2367 Lepidoptera species reported to occur in the province of Alberta, Canada, based on examination of the major public insect collections in Alberta and the Canadian National Collection of Insects, Arachnids and Nematodes. Records from relevant literature sources published since 1950 and from selected older works are also included. The entry for each species includes the scientific name, the author and year of publication of the original description, occurrence status, provincial distribution (according to ecoclimatic region), and adult phenology. The most recent taxonomic references are given, and common names are listed for butterflies and conspicuous moth species. The sources of specimen- and literature-based records are provided for each species. An additional 138 species whose occurrence in Alberta is probable are appended to the list. For 1524 of the listed species and subspecies, annotations are given, with selected information on taxonomy, nomenclature, distribution, habitat, and biology. An additional section provides details on 171 species erroneously reported from Alberta in previous works. Introductory sections to the volume provide a general overview of the order Lepidoptera and review the natural regions of Alberta, the state of knowledge of their Lepidoptera faunas, 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. A bibliography and an index of genus-level, species-level, and subspecies-level names are provided. 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. Status is revised for the following taxa, which were previously treated as junior subjective synonyms or as subspecies and are herein raised to species status: Carterocephalus mandan (Edwards, 1863); Hesperia manitoba (Scudder, 1874); Colias elis Strecker, 1885; Nymphalis j-album (Boisduval & LeConte, [1835]); Euphydryas bernadetta Leussler, 1920; Speyeria leto (Behr, 1862); Boloria myrina (Cramer, 1777); Coenonympha inornata Edwards, 1861; Colostygia circumvallaria (Taylor, 1906); Xanthorhoe delectaria Cassino & Swett, 1922; Xanthorhoe lagganata Swett & Cassino, 1920; Scopula quinquelinearia (Packard, 1870); Spodolepis danbyi (Hulst, 1898); Hyalophora gloveri (Strecker, 1872); Smerinthus ophthalmica Boisduval, 1855; Furcula borealis (Guerin-Meneville, 1844); Furcula occidentalis (Lintner, 1878); Acronicta cyanescens Hampson, 1909; Oligia rampartensis Barnes & Benjamin, 1923; Anarta nigrolunata Packard, 1867; Anarta columbica (McDunnough, 1930); Anarta montanica (McDunnough, 1930); Leucania dia (Grote, 1879); Euxoa adumbrata thanatologia (Dyar, 1904); and Euxoa furtivus (Smith, 1890). The following new synonymies are proposed, with the valid name presented first: Xanthorhoe algidata (Moschler, 1874) (= Xanthorhoe dodata Cassino & Swett, 1920), Macaria signaria (Hubner, 1809) (= Melanolophia unipunctaria W. S. Wright, 1916; Semiothisa marmorata Ferguson, 1972; Macaria? submarmorata Walker, 1861), Speranza occiduaria (Packard, 1874) (= Diastictis andersoni Swett, 1916), Caenurgina crassiuscula (Haworth, 1809) (= Caenurgina distincta (Neumoegen, 1884)), Tarache augustipennis Grote, 1875 (= Conacontia flavicosta Smith, 1900), Acronicta dactylina Grote, 1874 (= Acronicta hesperida Smith, 1897), Acronicta grisea Walker, 1856 (= Acronicta tartarea Smith, 1903), Acronicta lupini Grote, 1873 (= Merolonche ursina Smith, 1898), Fishia yosemitae (Grote, 1873) (= Fishia enthea Grote, 1877; Fishia betsia Smith, 1905; Fishia instruta Smith, 1910), Sutyna privata (Walker, 1857) (= Anytus profundus Smith, 1900), Mniotype ducta (Grote, 1878) (= Xylophasia versuta Smith, 1895), Mniotype tenera (Smith, 1900) (= Xylophasia miniota Smith, 1908; Hadena ferida Smith, 1908), Anarta decepta (Grote, 1883) (= Trichoclea postica Smith, 1891), Protorthodes incincta (Morrison, 1874) (= Taeniocampa utahensis Smith, 1888; Orthodes akalus Strecker, 1898). The following revised synonomy is proposed, with the valid name presented first: Xanthorhoe lagganata Swett & Cassino, 1920 (= Xanthorhoe incursata var. harveyata Cassino & Swett, 1922). One new generic synonymy is proposed, with the valid name appearing first: Idia Hubner, 1813 (= Reabotis Smith, 1903), resulting in one new combination. Six species are transferred from Trichoclea Hubner to Sideridis Hubner, resulting in six new combinations.