This work is the first in a series of catalogues on the bryophytes of the oldest National Forest of the USA, the Shoshone National Forest. Bordering Yellowstone National Park and being a part of the Greater Yellowstone System, the Forest has retained a wide spectrum of its pristine representative areas, which support a unique bryophyte flora. Based on over 4600 specimens, the catalogue of the bryophytes of the Wyoming's Beartooth Plateau, the northernmost territories of the Forest, has been produced. This bryoflora is composed of 282 species (45 liverworts and 237 mosses) in the study area, representing approximately 53% of the Wyoming bryophyte flora. The richness of the flora is due to the high diversity of habitats, caused by the geological history of this portion of the Central Rocky Mountains, location of the study area essentially in the subalpine and alpine belts, climatic and hydrologic features, and low anthropogenic disturbance. The high elevations and associated habitat conditions allow for many disjunct arctic-alpine species (approximately 25% in the bryophyte flora). Remarkable extensions of upper elevation limits for 72 taxa are registered. Fifteen species, two subspecies, and two varieties of liverworts, as well as 56 species and eight varieties of mosses have not previously been reported for Wyoming in Flora of North America and Synopsis of Liverwort Flora of North America North of Mexico. Thirty-nine taxa (five species of liverworts and 32 species and two varieties of mosses) are of potential conservation concern in Wyoming, including two rare species with Pacific coastal affinities, Philonotis yezoana Besch. & Cardot and Sphagnum miyabeanum Warnst., and one species of extreme northern habitats, Sciuro-hypnum glaciale (Schimp.) Ignatov & Huttunen, being a novelty for continental North America. Brachythecium erythrorrhizon Schimp. var. alpinum Kosovich-Anderson & Ignatov was recently described, using material collected as part of this study.