"Rates with Dirac's book as one of the best expositions of quantum theory available in the English language." — American Scientist "A fine translation of a remarkable book, which is recommended to every serious student of theoretical physics." — F. J. Belinfante, Science "Full and leisurely development ... detailed without being tedious ... This is a book that all who study quantum theory will want to read." — J. Polkinghorne, Physics Today "Throughout one is conscious of being under the guidance of someone who has thought very deeply and carefully about all the various aspects of quantum theory, and who is able to express his ideas in a most stimulating and lucid way." — K. W. H. Stevens, Proceedings of the Physical Society A masterful treatment of quantum theory, this classic work develops the subject's most important concepts from experimental evidence and from theory related to the wave nature of free particles. The first half shows how the classical mechanics of point particles can be generalized into a consistent quantum mechanics; the second part deals with extensions of quantum theory needed for problems of atomic and molecular structure. Suitable for advanced undergraduates and graduate students in physics as well as historians of modern science, this universally praised translation will be a valuable addition to any physical science library.