The objective of this book is to bridge a gap in the freshwater malacology of Venezuela which includes native, endemic and introduced species. A special effort has been set on species playing the role of intermediate hosts of important trematodiasis infecting cattle and humans in Venezuela. Gastropods are the most important group of molluscs including 49 species of which 11 may be considered as endemic, 28 as native and 10 as introduced. Bivalves include 16 species of which 3 may be considered as endemic, 11 as native and 2 as introduced. A state of the art is presented for each species: morphological description including shell morphology, anatomy of the reproductive system, phylogenetic data and genetic diversity when available, type of habitat and ecology. Since many of the treated species are distributed in large parts of Southern and Central America this book delivers an useful tool for the determination of freshwater molluscs in most parts of Central and Southern America.