First published in 1961, this book gives an account of the theory of the physical properties of the ions of metals having partly filled d shells in some or all of their compounds. It concentrates on non-cooperative phenomena, such as paramagnetism and single optical spectra, but a study of the theory is also desirable to an understanding of cooperative phenomena, such as ferro- and anti-ferro-magnetism. The extensive development and use of techniques in the theory of finite groups and their matrix representations is noteworthy. It leads to simple methods of deducing many known and new results and to the formulation of general theorems. While the book will be of interest primarily to mathematical physicists and theoretical chemists, the large amount of data in it, including 80 tables, will make it a valuable reference book for inorganic and physical chemists, biochemists and experimental physicists.