This book summarizes results and also the potential of separation of fluids through nonporous membranes. Two membranes separation techniques are involved, namely the pervaporation and the gas or vapor separation. Special attention is focused on ionic liquids. The ionic liquids can act as a separation medium in the form of supported ionic liquid membranes or selective components of a mixed membrane matrix. Moreover, the ionic liquid can successfully be used as a new class of solvent for chemical reactions. Their main advantage in downstream separation processes is negligible vapor pressure at...