Metal-organic frameworks (MOFs) are attracting much attention as promising materials for gas separation. Given the large number of design possibilities in the MOF materials space, it is desirable to efficiently characterize their performance prior to their experimental synthesis. This Perspective focuses on some of the works that have been put forth in developing new methods that accurately describe the thermodynamics of gas uptake in MOFs by making use of a few selected ab initio calculations. We provide a future outlook toward a full ab initio description of these properties using efficient sampling strategies in conjunction with faster and more accurate quantum methods. (c) 2015 Wiley Periodicals, Inc.