A review. The prepn. and characterization of novel composite membranes for size- or charge-based membrane sepn. processes with higher selectivity are described. Com. available porous membranes are used as support for thin layers of self-assembled block copolymers. The tailored diblock or triblock copolymers are synthesized by living ionic or controlled radical polymn., so that they can form microphase-sepd. nanostructures which may even be aligned into cylindrical morphologies with the characteristic axis perpendicular to the film surface. Supported nanoporous films may then be obtained either via the selective dissoln. of another polymer which had been added to form a polymer blend and which is compatible with the block of the copolymer forming the cylindrical domains, or via selective degrdn. of the copolymer block forming the cylindrical domains. Depending on the precursor block copolymer those pores may depend on the pH so that permeability and selectivity can be controlled by size or charge.