This review article discusses mainly the relationship between the chemical structure of new macromolecules synthesized for permselective membranes and their permselectivity, published over the period of twelve years, from 1985 to June 1996. Therefore, this review deals with macromolecules having well-defined structures and with permselective membranes whose separation mechanisms depend on the chemical structures of the membrane polymer. This review describes oxygen permselective membranes which concentrate oxygen in air, ethanol permselective membranes which concentrate ethanol in dilute aqueous ethanol solution, and optical resolution membranes which concentrate one enantiomer in racemates. In addition, permselective membranes whose permeability or permselectivity are controlled by external stimulation are also described.