The contributions of separation to human society cannot be underestimated. Majority of chemicals that are an essential part of our life are synthetics manufactured by different techniques. These range from foods, pharmaceuticals, and colorful dyes for our clothes to detergents for washing and cleaning. It is an established fact that much of these activities involved in the manufacture of the synthetics are causing damage to the delicate balance in the ecosystem. Developments in green technologies are not just academic curiosities but are increasingly nding commercial applications. Widespread use of natural resources has led to depletion of nonrenewable energy sources. There is an ever-increasing awareness about optimum utilization of the nonrenewable sources (NRS). One major cause of consumption of the NRS in the chemical process industries (CPI) is the use of fossil fuels as the source of heat in various processes. Separation processes are an integral part of the CPI. Among the various separation processes used in the CPI, the major consumer of fuels is distillation. It is impossible to build a chemical plant without using distillation at some point in the process. Even isolation of natural products such as essential oils, spices, and phytochemicals cannot be accomplished without distillation. Distillation as commonly employed uses a high-grade heat in the reboiler and rejects the same as very low-grade heat in the condenser. With the awareness about efcient utilization of these fuels, the CPI is looking at alternatives to this highly energy-intensive operation. Thus, membrane separations that either do not involve a phase change or use low-grade heat for the phase change are becoming increasingly important alternative to distillation. Several newer, promising approaches have been made in the recent past. Membrane-based separation techniques include microltration (MF), ultraltration, nanoltration, reverse osmosis (RO), pervaporation (PV), and vapor permeation (VP). PV based on differential permeation through a dense membrane followed by evaporation is the subject of this chapter.