A prominent figure in twentieth-century physics, Gregor Wentzel made major contributions to the development of quantum field theory, first in Europe and later at the University of Chicago. His Quantum Theory of Fields offers a knowledgeable view of the original literature of elementary quantum mechanics and helps make these works accessible to interested readers. An introductory volume rather than an all-inclusive account, the text opens with an examination of general principles, without specification of the field equations of the Lagrange function. The following chapters deal with particular field types that, by means of quantization, are associated with particles of various spin, charge, and mass values. Topics include scalar fields, the vector meson field, quantum electrodynamics, and the quantization of the electron wave field according to the exclusion principle. Clear and coherent, this text presumes a familiarity with the fundamentals of elementary quantum mechanics, and particularly with Dirac’s wave mechanics of spin-electrons.