This book presents the fundamentals of bonding in polyoxometalates and related oxides based on classical bonding concepts and the bond valence model. The in-depth treatment includes a revision of the procedure for the determination of the parameters of bond length-bond valence functions, the application of the bond valence model to polyoxometalates and related oxides, and the explanation of the distribution of the bond valences, and hence of the bond lengths, over the metal-oxygen bond and of the ionic charge on the oxygen atoms. Numerous tables and figures underline and illuminate the results. The principal author is a leader in the field of polyoxometalate chemistry. This work provides for the first time a comprehensive analysis of the structure and bonding in polyoxometalates, based on classical chemical concepts and the bond valence approach, and as such is a valuable resource for chemists, physicists and material scientists working in the field.