This is the first of three volumes describing and illustrating more than 1000 species of Australian mosses. Together, these volumes will represent the first national account of these diverse and ecologically significant organisms. The main features of ""Flora of Australia Volume 51: Mosses 1"" are: an introduction documenting 200 years of research on Australian mosses; moss classification and an overview of morphology and sexuality; an account of ecology and biodiversity; the origin and evolution of mosses; fossil bryophytes; and a key to the more than 300 genera of mosses known from Australia and its island territories. The volume includes descriptions of 22 families, 42 genera and 238 species and infraspecific taxa, including synonymy, specimen citations and notes on habitat and distribution. Distribution maps are provided for each species and infra-specific taxon, as well as more than 50 pages of line-art illustrating habit and anatomy and 64 colour photographs.