This cover showcases the mixed-matrix membranes (MMMs) incorporating metal–organic framework (MOF) porous materials that are used for efficient gas and oil-water separation in the petrochemical industry. These membranes represent a significant breakthrough and transformation in separation engineering, due to the advancement of engineered materials based on MOFs in recent years. The porous MOF materials endow MMMs with versatility and diversity, as well as superior separation performance. This special issue examines various strategies that integrate porous materials and polymer matrices to enhance interfacial morphology and achieve equilibrium-kinetic combined selectivity.