Quantum Chemistry covers the basic principles, methods, and results of quantum chemistry, providing insights on electron behavior. This book is organized into 14 chapters that focus on ground state molecular orbital theory. After briefly dealing with some of the concepts of classical physics, the book goes on describing some simple but important particle systems. It then examines several systems with discontinuous potential energies, such as the simple harmonic oscillator and the hydrogen-like ion system. A chapter presents a set of postulates and theorems that form the formal foundation of quantum mechanics. Considerable chapters are devoted to various quantum chemical methods, as well as their basic features and application to molecular orbital evaluation. These methods include Huckel molecular orbital, variation, linear variation, extended Huckel, and SCF-LCAO-MO. The concluding chapters deal with the development of theories for molecular orbital, including time-independent Rayleigh-Schrodinger perturbation, group, and qualitative molecular orbital theories. Supplemental texts of the more complicated derivations or proofs and problems encountered in quantum chemistry are also provided. This book is an introductory text intended for organic, inorganic, and physical chemists, as well as for graduate and undergraduate students.