The Fissidentaceae are acrocarpous mosses. The family, consisting of only the genus Fissidens, is represented in the neotropics by 93 species, of which 62% are endemic. This book includes introductory material about the taxonomic history, morphology, phylogeny. Full descriptions, nomenclature, identification keys are provided for the 93 neotropical species. One new species, F. ecuadorensis, is described. Four new synonyms and 22 new lectotypes are designated. Distribution Maps and illustrations are provided for most species.