Based on surveys in the Leningrad and Novgorod Regions the peculiarities of pearl mussel habitats are discussed: rivers with pearl mussels in the northern part of the range take source in lakes, but not from springs or mires; archival data on pearl fishing do not provide any exact information on pearl mussel distribution (data from 19th century and earlier sources are the most specific); in most of their range pearl mussels do not inhabit rivers with hard water although they can endure some increase in water hardness caused by human impact; pearl mussels rarely coexist with other freshwater bivalves (some cases of such coexistence have appeared because of maninduced changes in river ecosystems); rivers with pearl mussels feature a complex of specific microhabitats. With these patterns in mind one can more efficiently search for pearl mussel populations in Russia.