Preface -- Point defects -- Atomic mobility: diffusion -- The atomic theory of diffusion -- Non-stoichiometry and point defects -- Fast ion conductors -- Non-stoichiometry and electronic conduction -- Defects and optical properties -- Defects, composition ranges and conductivity -- Point defects and planar defects -- Defects and non-stoichiometry in high temperature superconductors -- Non-stoichiometry: an overview.