Molecular sieve membranes are characterised by their high thermal and chemical resistance and by their monodisperse micropore system. Mixtures can be separated according to molecular size as well as according to adsorptive interactions and diffusion differences. This paper outlines techniques for reproducible production of large area membranes together with methods for their regeneration and repair. Typical separations demonstrate the efficiency of these membranes. Potential application fields can be deduced from developmental trends.