This catalogue is the result of a four-year survey of the mollusks of Jeju Island, the southernmost island in the Republic of Korea. Forty-eight survey stations were visited, with a total of 82 specific localities being sampled. Literature records were also obtained. Local and world distribution of each species is included. This survey reports a total of 1,072 mollusk species and subspecies; 1,015 marine and 57 land and freshwater. There are 812 gastropods, of which 755 are either entirely marine or have marine affinities. The best represented of the marine families are the Pyramidellidae, Trochidae, and Ovulidae. There are 225 bivalves, none being freshwater species, with the Veneridae, Mytilidae, and Arcidae having the largest number of species. Among the smaller classes there are sixteen Cephalopoda, eleven Polyplacophora, and eight Scaphopoda. Compared to mainland Korea, Jeju Island has a rather small terrestrial mollusk fauna and a depauperate freshwater one, with mainly Palearctic connections. The Helixarionidae and Bradybaenidae are the largest terrestrial families. The marine faunal affinities with the neighboring Japonic and Indo-West Pacific provinces are also discussed, revealing that this island’s mollusk fauna is a blend of warm-temperate and subtropical-tropical species.