The book presents all European species of molluscs*, which are about 2090 snails and 53 mussels. In several groups the species definition is controversial, others are currently in a state of taxonomic revision. So the number of species can only be approximated. Surprisingly many groups in Europe are relatively little studied. This includes, for example, the large species of the genus Helix which are the only snails that have importance in the human diet.
Europe includes Cyprus and Turkey's western regions, but not the eastern Atlantic islands (Canary Islands, Madeira, Azores) and the Caucasus region. In the east the area extends approximately to the Moscow region. Iceland is also included.

*all species without about 400 species of hydrobioids, which are very small snails of freshwater sources with extremely restricted ranges, and which are practically only known to the specialists.