Metal-organic frameworks (MOFs) are nanoporous materials with potential applications in adsorption separations, catalysis, and gas storage. They are synthesized in a “building-block” approach by self-assembly of metal or metal-oxide vertices interconnected by rigid organic linker molecules. Several MOFs have been shown to exhibit interesting CO2 adsorption behavior and have high adsorption capacity. Using computational modeling tools we have screened a wide variety of MOFs for CO2 adsorption, including MOFs of various topologies, metal corners and organic linkers. Adsorption isotherms were calculated from atomistic grand canonical Monte Carlo simulations. Mixture simulations or single-component isotherms plus ideal adsorbed solution theory were used to investigate the selective adsorption of CO2 over other gases such as N2, CH4 and H2 to explore separations such as the removal of CO2 from flue gas. Comparisons of predicted single-component isotherms and heats of adsorption with experiment were made where possible. In addition, we are designing new hypothetical MOFs by modifying existing MOFs, for example by proposing new linkers, and simulating their adsorption performance.