Pervaporation is one of the most active areas in membrane research, and the pervaporation process has been shown to be an indispensable component far chemical separations. In this paper, the recent development in pervaporation membranes and pervaporation processes is reviewed, and some outstanding questions involved in membrane pervaporation are discussed with emphasis on the following issues : mass transport; in the membrane, membrane material selection, concentration polarization in the boundary layer, pressure buildup in hollow Fiber membranes, asymmetric and composite membranes, and the activation energy for permeation, We attempt to provide insight into this dynamic field and to highlight some of the outstanding problems yet to be solved or clarified.