The monograph outlines the foundations of modern ideas and methods for studying the electronic structure and properties of coordination compounds - the theory of the crystalline field, the method of molecular orbitals, the theory of electron-vibrational (vibron) interactions, electronic spectra and some applications of the theory to the issues of stereochemistry and crystal chemistry, stability, reactivity, and chemical reaction mechanisms. The second edition added sections outlining the properties of f-electrons and the splitting of their corresponding terms in crystalline fields; The description of the LCAO ME methods has been expanded with an analysis of their capabilities and limitations and a brief overview of specific results; a new method for calculating the electronic structure of polyatomic systems is presented - the Slater-Johnson Xa-method; a chapter on electron-oscillatory interactions and the Jan-Teller effect and sections on photoelectron spectroscopy, crystal chemistry and chemical reaction mechanisms were supplemented and re-written.