The text is concerned with classical aspects of Physical Chemistry - bonding, thermodynamics, kinetics, electrochemistry - applied, however, to the Solid State. Special emphasis is placed on (and in fact two thirds of the book are devoted to) the role of the ionic and electronic charge carriers. These are elementary deviations from the perfect state and the relevant centers with regard to chemical kinetics and electrochemistry. The presentation is based on modern material examples comprising ion conductors, electronic conductors, mixed conductors and superconductors, and discusses the fundamentals necessary for the understanding of electrochemical devices such as sensors, batteries and fuel cells.