The genus PhlaeopterusMotschulsky, 1853 is revised, and a key to the 18 valid species is provided. Eight new species are described: Phlaeopterus obsoletus Mullen and Campbell, new species; Phlaeopterus kavanaughi Mullen and Campbell, new species; Phlaeopterus bakerensis Mullen and Campbell, new species; Phlaeopterus smetanai Mullen and Campbell, new species; Phlaeopterus occidentalis Mullen and Campbell, new species; Phlaeopterus olympicus Mullen and Campbell, new species; Phlaeopterus hatchi Mullen and Campbell, new species; and Phlaeopterus elongatus Mullen and Campbell, new species. Two species, Phlaeopterus kootenayensisHatch, 1957, and Phlaeopterus stacesmithiHatch, 1957, are transferred to the genus UnamisCasey, 1893. The monotypic genus VellicaCasey, 1885 is synonymized under Phlaeopterus, new synonymy.Phlaeopterus rufitarsusCasey, 1893 is synonymized under Phlaeopterus filicornisCasey, 1886, new synonymy.Phlaeopterus cascadiensis is demoted to a subspecies of Phlaeopterus castaneus (Casey, 1893), new synonymy and new status. Phlaeopterus brevipennisCasey, 1893 and Phlaeopterus longipalpusCasey, 1885 are synonymized under Phlaeopterus cavicollis (Fauvel, 1878), new synonymy. Lectotypes are designated for four species: Tilea castaneaCasey, 1893 (= P. castaneus); Tilea cavicollisFauvel, 1878 (= P. cavicollis); Vellica longipennisCasey, 1885 (= Phlaeopterus longipennis (Casey, 1885), new combination); and P. filicornis. Distribution data for each species are provided. Given these beetles' association with shrinking alpine snowfields, conservation concern is warranted, and some highly endemic species described herein have not been collected in over 35 years.