Reverse electrodialysis (RED) is an emerging membrane based energy conversion process used to extract electricity by mixing two water streams of different salinities. This technique utilizes transport of cations and anions during controlled mixing of saltwater and freshwater through selective ion exchange membranes. The development of ion exchange membranes and optimization of system performance are crucial for sustainable energy capture from salinity gradients using RED. Recently, increased attention has been given to the preparation of ion exchange membranes and to understanding the factors that determine the RED power performance. This review evaluates potential ion exchange membrane materials, currently available state-of-the-art RED membranes, and their key properties. Discussion will focus on the electrochemical and physical properties of these membranes (e.g., resistance, permselectivity, and swelling) because of their significant role in RED performance throughout the system, Although an interconnected relationship exists between membrane properties, RED requires high quality membranes that are uniquely tailored to have a low resistance and high permselectivity. Moreover, harnessing this potential technology demands not only carefully optimized components but also a novel RED stack design and system optimization. The key findings and advancements needed to assure proper stack design and optimization are also described. This review paper's goal is to elucidate effective energy conversion from salinity gradients and expedite implementation of RED as the next promising renewable source of power for large-scale energy generation. (C) 2015 Elsevier B.V. All rights reserved.