Book excerpt: Solid-state electrochemical devices, such as batteries, fuel cells, membranes, and sensors, are becoming pervasive in our technologically driven lifestyles. The development of these devices involves common research themes such as ion transport, interfacial phenomena, and device design and performance, regardless of the class of materials or whether the solid state is amorphous or crystalline. However, results of recent research in this field tend to be presented in symposia separated along the lines of particular solidstate materials disciplines rather than by phenomena controlling device performance. The papers in this issue of ECS Transactions were presented at the fifth of a series in international symposia "Solid-State Ionic Devices V", at the 212th Electrochemical Society Meeting, in Washington DC, October 7-12, 2007. The intent of the symposia was to provide a forum for current advances in ionically conducting materials and devices that is organized along phenomenological lines, rather than by specific material discipline. The papers in this issue range from the fundamentals of ionic and mixed ionic-electronic transport to device performance and are in keeping with that intent.