This review deals with the problem of mollusk invasions into the inland waters of the Western Siberian region. The data on all the alien species of snails and bivalves registered up to now in water bodies of the region are provided. Possible ways and mechanisms of penetration of the alien species into the Western Siberian water bodies are discussed. The most well-studied case of mollusk invasion, that of the European river snail, Viviparus viviparus (L., 1758), into water bodies of the Ob-Irtysh basin, is considered in detail. An ecological and geographical classification of the invader species is proposed. It includes three categories: (1) exotic species, (2) species belonging to the boreal European complex which regain the lost part of their range, and (3) heat-loving species of South European origin. We hypothesize that, in the foreseeable future, the inflow of the alien mollusk species to the Western Siberian inland waters will remain low owing to some physical-geographical peculiarities of this area.