The Aral and Caspian Seas belong to the group of the world's largest brackish water basins that are characterized by a long geological history and unique biota, including a rich and diverse fauna of molluscs (bivalves and gastropods). Though the history of scientific exploration of the Aralo-Caspian malacofauna can be traced back to the end of the 18th century, there is still a lack of a comprehensive and illustrated survey of the Mollusca of these two sea basins. The book provides an annotated inventory of the recent Bivalvia and Gastropoda of the Aral and Caspian Seas, with their synonymy, notes on ecology and distribution, and images of shells (including numerous images of type specimens - holotypes, lectotypes, syntypes, etc.). An extensive overview of the physical geographical conditions of the two basins as well as their geological history is provided alongside an outline of the historical development of their malacofaunas. The systematic part contains a description of the fauna, represented in the Aral Sea by two species of Gastropoda and seven species of Bivalvia, and in the Caspian Sea by 33-34 species of Bivalvia and 63 species of Gastropoda. These estimates, however, are of provisional character only, since the high level of taxonomic uncertainty makes it impossible to determine exactly the actual number of living species. A special discussion is devoted to the drastic degradation of the Aralo-Caspian malacofauna in the former century, which was caused primarily by the anthropogenic destruction of the aquatic environment and the inflow of alien molluscan species.