Protonic conduction in liquid electrolytes is commonplace but is relatively rare in solids. There is currently much interest worldwide in proton conducting solids, both from the scientific aspect, as materials with novel properties, but also for their possible applications in high density solid-state batteries, sensors and other electrochemical devices. This book gives a comprehensive review of proton conductors, including theory, techniques, the materials themselves and applications. The first part of the book describes chemical and physical parameters necessary for fast proton conduction and proposes a classification of different kinds of proton conductors. Comparison is made with other hydrogen-containing materials such as metals and graphites. The importance of partial water pressure, the role of defects and surface phenomena are discussed. The second part treats the chemistry, structures and electrical properties of typical materials from hydrogen bronzes to polymers via ice, hydroxides, acid sulphates, layer hydrates, clays, gels and porous or fractal media. The third part of the book discusses the methods concerning the proton dynamics from local to macroscopic scale. The fourth part deals with conductivity and concludes with a discussion of applications such as electrochemical systems for energy production or storage and microionic devices. This book will be of interest to all those working in the solid-state ionics community. The readership is likely to include chemists, physicists, material scientists, both in industry and at the research level.