Professor of Theoretical Physics at Birkbeck College, University of London, provides a formulation of the quantum theory in terms of qualitative and imaginative concepts that have evolved outside and beyond classical theory. Although it presents the main ideas of quantum theory essentially in nonmathe-matical terms, it follows these with a broad range of specific applications that are worked out in considerable mathematical detail. Addressed primarily to advansed undergraduate students, the text begins with a study of the physical formularion of the quantum theory, from its origin and early development through an afalysis of wave vs. particle properties of matter. In Part II, Professor Bohm addresses the mathematical formulation of the quantum theory, examining wave funecions, operators, Schrödinger's equation, fluctuations, correlations and eigenfungions. Part Ill takes up applications to simple systems and further extensions of quantum theory formalation, including matrix formulation and spin and angular momentum. Parts IV and V explore the methods of approximate solution of Schrödinger's equation and the theory of scattering. In Part VI, the process of measurement is examined along with the relationship between quantum and classical concepts. Throughout the text, Professor Bohm places strong emphasis on showing how the quantum theory can be developed in a natural way, starting from the previously existing classical theory and going step by step through the experimental facts and theoretical lines of reasoning which led to replacement of the classical theory by the quantum theory. Unabridged Dover (1989) republication of the edition.