Book excerpt: Methods of Molecular Quantum Mechanics This advanced text introduces to the advanced undergraduate and graduate student the mathematical foundations of the methods needed to carry out practical applications in electronic molecular quantum mechanics, a necessary preliminary step before using commercial programmes to carry out quantum chemistry calculations. Major features of the book include: Consistent use of the system of atomic units, essential for simplifying all mathematical formulae Introductory use of density matrix techniques for interpreting properties of many-body systems An introduction to valence bond methods with an explanation of the origin of the chemical bond A unified presentation of basic elements of atomic and molecular interactions The book is intended for advanced undergraduate and first-year graduate students in chemical physics, theoretical and quantum chemistry. In addition, it is relevant to students from physics and from engineering sub-disciplines such as chemical engineering and materials sciences.