Over the next twenty-five years, global energy consumption is projected to grow by almost half, and electricity generation is expected to nearly double. The massive investment in infrastructure required to satisfy this demand presents a major opportunity for innovation in how energy is produced, stored, transmitted, and used. In particular, there is keen interest in sustainable energy technologies capable of improving efficiency and reducing environmental footprint. Membranes have the potential to play a significant role in a number of relevant separations applications, including CO(2) capture, energy storage, and water production for energy production. This article seeks to highlight opportunities for membranes-related R&D relevant to sustainable energy, of which the broader membrane community may not be fully aware. We pose some specific technical questions related to two topics - CO(2) capture in power generation, and water treatment for energy production - with the twin goals of stimulating thought and discussion within the broader membrane community, and sparking increased engagement between researchers and industrial end-users. This article is based upon a plenary talk on opportunities for membrane technologies in the context of sustainable energy, given at the 2010 NAMS/ICIM conference. (C) 2011 Elsevier BM. All rights reserved.