A revision of the genus Cymbiodyta Bed. (Hydrophilidae: Hydrobiinae) is presented including a short historical review and a discussion of diagnostic characters and techniques. Twenty-nine species are recognized. Twelve species and two subspecies are described as new. C. hatchi D. C. Miller, 1964 is placed in synonymy with C. pacifica Leech, 1948, and C. morata Horn, 1890, with C. dorsalis (Motschulsky, 1859). Neotypes are designated for C. vindicata Fall and C. acuminata Fall; lectotypes are designated for C. brevicollis (Sharp), C. fraterculus (Sharp), C. morata Horn, C. polita (Sharp), and C. blanchardi Horn.The genus is divided into 11 species groups. A key to species is provided. Each species is described and illustrated, and all available bionomic and distributional data are presented. Distributional records are mapped.