Solid state ionics is concerned with the science and technology of ions in motion in the solid state. Ions in motion may also involve electrons, depending on the materials and surroundings. These days, solid state ionics is finding an increasing variety of applications. The knowledge of solid state ionics is also extensively mobilized to protect, predict or elongate the lifetime of structural materials in harsh service conditions and to improve the performance reliability of devices. Furthermore, solid state ionics is now being combined with the emerging nanotechnology to produce new knowledge and applications. This book covers the following topics: fuel cells and membranes; batteries; sensors and electrochromics; fundamentals of ionic transport and defect chemistry; cation/anion/mixed ionic electronic conductors.