A taxonomic study was made of several North American taxa in the genusAtrichum. The primary emphasis was on the Canadian taxa and a key to the six species (A. altecristatum, A. angustatum, A. crispum, A. oerstedianum, A. selwynii, A. undulatum) and one variety (A. undulatumvar.gracilisetum) of the country is presented.Atrichum oerstedianum, which has been confused withA. undulatum, is added to the moss flora of the United States and Canada. The distribution ofA. crispumis clarified and a detailed study of the species revealed new morphological characters that are useful to distinguish it. A variety ofA. undulatum, the var.altecristatum, is raised to the rank of a species and morphological and distributional data are given to support the status ofA. selwyniias a distinct species. The first chromosome counts are reported forA. selwynii(n = 7) andA. altecristatum(n = 14). Detailed descriptions are provided forA. altecristatum, A. crispum, A. oerstedianum, andA. selwynii.