Mosses are special and ancient terrestrial plants. Due to their small size and limited taxonomic traits, many moss taxa are still taxonomically problematic. Macromitrium Brid. (Orthotrichaceae, Bryopsida), the third largest moss genus with almost a thousand species names, is a representative genus of taxonomically challenging taxa. The genus is most species-rich around the Pacific Ocean with a typical pan-tropical distribution. The present monograph is basically a type specimen-based systematic summary, mainly based on our taxonomical revisions on the genus in the past 20 years, partially on regional revisions of other bryologists. The book provides detailed and comprehensive information on 271 confirmed species, most with illustrations and some with color photos. This book brings together the latest findings of the genus Macromitrium and valuable reference for professionals and amateurs.