Polymers have become an inextricable part of our daily life. Not only the synthesis but also the processing of polymers has been given a major attention. Most of the commercial methods use environmentally hazardous volatile organic solvents (VOC)and chlorofluorocarbons (CFC) for processing and synthesis of polymers. Due to the enormous increment of VOC/CFC emissions and also the generation of aqueous waste streams, chemical engineers and chemists have already been looking for new and cleaner alternatives. One of these methods is the use of supercritical fluids as a processing solvent. An intense research activity concentrated in the last decade has demonstrated that dense carbon dioxide is an attractive solvent for polymer synthesis as it is environmentally benign, inexpensive, with tunable physico-chemical properties and substantially inert towards chain transfer reactions. We have briefly described the synthesis of different polymers and their nanocomposites with metal nanoparticles in supercritical carbon dioxide in this book.