Driven by the concerns over the dwindling supplies of petroleum and the dire consequences of global warming, the emergence of a hydrogen economy appears inevitable. Such development will require the advancement of separation technologies with significantly improved energy and cost efficiencies. Membrane technology is the ideal choice for hydrogen purification due to its lower power usage and costs, simplicity in operation, as well as compactness and portability. Assuming hydrogen purity requirements of < 99.5% and relatively modest operating temperatures, polymeric membranes are preferred among the various alternatives. Generally, polymeric membranes for hydrogen enrichment are either H-2- or CO2-selective, depending on the governing kinetic or thermodynamic factors. In this review, the current state-of-the-art for polymeric membranes applicable to hydrogen purification is considered, and the different approaches for enhancing intrinsic gas-separation performance are evaluated. An assessment of the benefits and shortcomings of the respective membrane types are presented, and the future directions most promising for the development of robust and high-performance polymeric membranes for the hydrogen economy are highlighted. (c) 2008 Elsevier B.V. All rights reserved