Electrodeionization is an ionic separation technology that initially emerged similar to 50 years ago. In an early application, it was utilized to remove metallic species from radioactive wastewater; however, a poor understanding of its functional kinetics has slowed its development and applications. Steadily increasing research efforts have focused on the elucidation of detailed operational mechanisms, thereby enabling the extension of its applications to other fields. To date, electrodeionization has been proven to be an excellent environmentally compatible purification, separation and concentration method. Novel materials have been continuously developed toward the improvement and maturation of this technology, which may lead to enormous environmental and economic benefits on a global scale. This comprehensive review examines the inception, precursor techniques and historic evolution of electrodeionization, as well as its underlying principles, advantages and promising applications in wastewater treatment and water purification. (C) 2014 Elsevier Ltd. All rights reserved.