This text presents a unified and up-to-date discussion of the role of atomic and molecular orbitals in chemistry, from the quantum mechanical foundations to recent developments and applications. Abundantly illustrated, the volume critically establishes the relationships between the more formal quantum mechanical formalisms and the traditional chemical descriptions of chemical bonding. It is mathematically less demanding than most traditional quantum chemistry texts, yet still retains clarity and rigor. This volume is an ideal textbook for any course in which chemistry is a significant part.