Separation of water from its mixtures with organic liquids, especially from those with which it forms azeotropes by means of pervaporation and vapour permeation. has matured during the past 10 years to a state-of-the-art technology. The processes are applied in industrial plants worldwide for the dehydration of binary mixtures of light alcohols such as ethanol or isopropanol, esters such as ethyl or butyl acetate (EtAc, ButAc), ketones such as acetone or 2-butanone, ethers such as tetrahydrofurane, nitriles such as acetonitrile or multinary mixtures of any of the previously mentioned organics. Of growing importance is the removal of water from reaction mixtures both to shift the respective reaction equilibrium toward the wanted product and to facilitate its separation and final purification.