The majority of natural, cold habitats occurred to be sources of psychrophilic and psychrotrophic microorganisms, producing cold-adapted enzymes. They exhibit high activity and catalytic efficiency at low and moderate temperatures, which results from the elevated flexibility of their molecules. Structural differences between psychrophilic enzymes and their counterparts originating from mesophiles and other organisms are rather subtle and do not involve changes of molecular catalytic mechanisms. Because of high activity at low temperatures and an increased thermolability they are attractive biocatalysts for many biotechnological purposes, some of which are presented in this paper.