Carbon molecular sieve membranes (CMSM) have gained increased interest in the last decade as they allow an excellent compromise between performance, in terms of permeability and separation factors, while exhibiting a very good chemical and mechanical stability. Their performance is nowadays better than commercial polymeric membranes, although their production costs are still higher and represent one of the main limitations for their large-scale exploitation. In this chapter, a comprehensive overview of CMSM is given, paying special attention to the transport mechanism of gases through these membranes, the equations describing this phenomenon, the strategies to follow for maximizing their performance, and finally the potential applications of these membranes.