Different types of membranes are considered: monolithic (non-porous), porous, liquid and biological (natural and synthetic), asymmetric and composite, as well as their areas of application. The experience of intensive development of membrane processes over the last quarter of a century is summarized. The main attention is paid to the influence of membrane structure on the characteristics of various membrane processes. The features of polymers that determine the properties of membranes are discussed. Recommendations are given for the manufacture of membranes of a certain structure. For scientific and technical workers engaged in the field of chemistry and physical chemistry of polymers, physicists, biotechnologists.