The use of membrane technology is developping from the solely work-up of product and waste streams all the way to integration into processes, The membrane reactor offers, by analogy with biological cells, great possibilities for product-integrated environmental protection. Two principal areas of application of membranes in reactors are becoming apparent, Use for removal of products or by-products from bioreactors acid the coupling with chemical reactions considered in this article. The first such membrane reactors served for the removal of water from esterification reaction mixtures, Significant advances for membrane reactor technology came with the recent development of membranes of enhanced selectivity and flow density as well as improved thermal and chemical stability. In addition to the availability of high-performance membranes, fundamental knowledge and methods are required to assure efficient reaction-engineering utilization of membrane reactors. This paper discusses fundamental concepts relating to the use of various membrane reactors in parallel, consecutive, and equilibrium reactions. In general, in the case of membrane-supported parallel reactions, controlled addition of reactant can raise the reaction selectivity. Selective removal of primary and side products from consecutive or equilibrium reactions can increase yields. Comparison of membrane-supported reactor types (batch, loop, and plug-flow membrane reactors) indicate that the membrane-supported loop reactor will prove most effective in the majority of cases thanks to its pronounced flexibility.