Subfossil mollusc shells are some of the most common remains in marine Quaternary sediments and can give precise information about the palaeogeographic conditions of palaeobasins. This is primarily due to their good preservation and the large number of species. They are widespread in nearly all biotopes and often occur in beach deposits, now lying at some distance inland above the present-day sea level. Molluscs are susceptible to the environment they inhabit and can therefore provide information about the substrata, water depth, salinity, temperature, isotopic composition of water and water-level fluctuations in ancient bodies of water. Molluscs can also be used in the stratigraphic subdivision and correlation of sediments. Conditions for the investigation of subfossil mollusc fauna in Estonia are extremely good. The bedrock in the coastal area consists mainly of limestones and dolomites, which are covered with carbonaceous till and limy aqueoglacial deposits. In Estonian offshore waters molluscs had suitable living conditions and sufficient material to build up the shells. In Estonia the Holocene mollusc fauna is much better preserved than in neighbouring countries.