Mixed-matrix membranes (MMMs), which combine porous materials with a polymeric matrix, have gained considerable research interest in the field of gas separation due to their complementary characteristics and cooperative activation. The tailorability and diversity of porous materials grant MMMs extendable functionalities and outstanding separation performance. To achieve the full potential of MMMs, researchers have focused on the rational matching of porous fillers with polymeric matrixes to achieve enhanced compatibility at the interfaces of these materials. In this review, we highlight state-of-the-art advances in combining metal–organic frameworks (MOFs) and metal–organic cages (MOCs) with polymeric matrixes to fabricate MMMs using different strategies. We further discuss the opportunities and challenges presented by the future development of MMMs, with the aim of boosting MMM fabrication with judicious material design and selection.