This book embraces the entire range of problems associated with nonstoichiometry, disorder and order in solids. Although dealing primarily with transition metal carbides, nitrides and oxides, the methods and models presented are applicable to all systems with substitutional disorder and they permit a unified approach to the structure, phase diagrams and other physical and chemical properties of these systems. This book will be useful for physicists addressing the problems of order and disorder in solids, for chemists increasingly aware that the majority of natural and synthetic materials are nonstoichiometric, and for crystallographers studying new and unusual crystal structures. Materials scientists using refractory compounds to create novel superhard and tough materials or materials for modern electronics will find essential information on the interplay between structural effects and many different properties of transition metal compounds.