Intriguing plant life on the world's most remote inhabited island... The historic collections of liverworts and hornworts of the Tristan da Cunha group of islands in the South Atlantic Ocean were examined together with the heretofore-unstudied large collections of Niek Gremmen (Diever, Netherlands) and James Dickson (Glasgow, United Kingdom). For each of the 145 taxa included here, the authors provide taxonomic and nomenclatural remarks where pertinent, a statement of distribution, lists of literature records, ecology, and selected specimens cited. Other features: a history of hepaticological exploration; an account of the island's phytosociology; an assessment of phytogeographic affinities of Tristan-group liverworts and hornworts; and description of new taxa (2 genera, 5 species, 2 ingraspecific); 9 new combinations.