Solid state ionics, being a multidisciplinary area, is expected to grow at a faster rate in the new millennium, prompting the discovery of new materials and devices, as well as helping to optimize the known devices, especially the portable power sources and display systems. The Asian Society for Solid State Ionics (ASSSI) plays a significant role in bringing together researchers from the Asian countries, every two years, to exchange notes and ideas, to foster friendship and collaboration, and to discuss the prospects.The topics covered in this volume are: ion dynamics, theoretical modeling, ion-conducting polymers, gels and ceramics, glasses, crystalline materials including nano-phases, composites, electrode/electrolyte interfaces and novel experimental techniques. Papers on crystalline materials deal with ion conduction in Li, Na, Ag, Tl, F and O-containing compounds. Materials and device aspects have received wide coverage, especially the areas of lithium ion batteries (LIBs) and solid oxide fuel cells (SOFCs).Rechargeable high energy density LIBs, especially those employing immobilized gel or polymer electrolyte, are the favorite portable power sources in the new millennium. As expected, a large number of papers on both cathodes and polymer electrolytes for LIBs were presented at the conference. The papers on fuel cells almost exclusively deal with SOFCs, indicating the great importance being given to this area in Japan and China. A breakthrough in materials and technology of SOFC is expected in the coming decade. This volume will be useful not only to the active researchers in the field but also to youngsters entering the exciting area of solid state ionics.