The aim of this book is to present an outline of the principles of quantum mechanics that are fundamental in understanding the properties of molecules.

The text is structured in such a way as to guide an undergraduate reader from the point where the shortcomings of classical physics are recognized to the construction and application of a theory that seems adequate in interpreting the spectra and the electrical and magnetic properties of molecules.

The emphasis of the latter sections of the book is on properties rather than on the structure of molecules, as there is already a large number of excellent books that address structure. Attention has also not been given to the theory of chemical reactions, because while extremely interesting, it is still at a low level of development.

The theory of chemical bonding cannot be ignored, but the chapter in which it is included aims to present the principles of chemical bonding and not detailed explanations.