The book summarizes modern knowledge on the river crayfish of Belarus, represented by two native species - long-toed and wide-toed crayfish and one alien - striped crayfish. The current distribution of crayfish has been analyzed, there is a continuing decrease in the number of the Red Book species - wide-toed cancer and the widespread distribution of long-toed cancer in the reservoirs of Belarus. Rapid colonization of reservoirs with a foreign invasive species - striped cancer is stated. Growth was studied, reproductive parameters of native species were estimated. The production and total mortality of individuals of the sexually mature part of the long-toed cancer populations have been determined. Ways and methods of protecting and increasing the number of crayfish have been analyzed.