The Fissidentaceae are recognized to include a single genus, Fissidens, which is divided into four subgenera, Aloma, Fissidens, Octodiceras, and Pachyfissidens, on the basis of new taxonomically useful characters i.e., peristome type, costa type, and number of files of exothecial cells. Subgenera Aloma and Octodiceras are not subdivided. Subgenus Fissidens consists of sections Fissidens and Sarawakia, comb. nov. Subgenus Pachyfissidens is divided into three sections: Amblyothallia, comb. nov., Crispidium comb. nov., and Pachyfissidens. The most primitive species of the genus are found in section Amblyothallia, while the most advanced species are in subgenera Aloma and Octodiceras. A key to the subgenera and sections is provided.