Nanomaterials have tremendous potential in a wide variety of membrane applications. Within the vast range of nanomaterials, there are many cases of dense and porous membranes with exceptional strength and tailored surface properties, which can be extremely light or thin. Currently, graphene-based membrane materials (e.g., nanoporous graphene, graphene oxide (GO), and graphene- or GO-embedded polymers) hold great promise for membrane-based gas separations. For the last decade, significant advances have been made on the development of graphene-based membranes for gas separation via both a large number of theoretical studies and some proof-of-concept experiments. Theoretically, graphene-based membranes can afford remarkably high gas permeance and selectivity with notable mass-transport properties that may be not possible with state-of-the-art commercial polymeric, inorganic, and ceramic membranes. Prompted by these theoretical calculations, as well as the unique physical-chemical properties of graphene, many experimental approaches have been extensively explored to make these membranes a reality for practical processes. In this chapter, the latest achievements on both theoretical and experimental studies of graphene-based membranes are discussed in relation to gas separation applications.