Separation of gas mixtures by adsorption is a well established separation process technology and is used to serve chemical, petroleum and material processing industries. In addition to above applications, it also presents opportunities for reducing green house gas emissions and cost reductions via efficient separation and reuse of waste gas mixtures. Innovations in sorbent development and adsorption process cycles have made zeolites as a key separation tool for industries. This monograph provides a single and comprehensive source of knowledge for cation modified zeolite-A, Zeolite-X, and Zeolite ZSM-5 based adsorbents for carbon monoxide, methane and nitrogen gas mixture separation. This monograph also presents basics of gas separation, ion exchange and deals with interactions between gas molecules and zeolites. The undertaken studies are highly significant and enhance our knowledge and understanding of mechanisms of gas separation by zeolites, and present their potential applications for separation of different gas mixtures. This monograph will enhance the reputation and attractiveness of zeolites for researchers working in the field of adsorbent development for gas separation.