This concise, highly regarded text on the nature of orbitals, terms, and states offers a fine introduction to quantum chemistry. The treatment is especially suitable for students with a limited mathematical background. Topics include atomic and molecular spectroscopy, quantum mechanics, and bonding theory. More briefly covered are the expansion theorem and the concept of basic functions, perturbation theory and the variational principle, secular equations and determinants, Slater determinants and antisymmetry, and real versus complex orbitals. Based on the author’s years of teaching experience, the mathematical explanations are presented as simply as possible, and the more difficult subjects are explained fully. An excellent supplement to any chemistry text for undergraduate students in chemistry and related fields.