Quantum Theory, III: Radiation and High Energy Physics focuses on the fundamentals and applications of quantum theory. The selection first offers information on relativistic wave equations and noncovariant quantum theory of radiation, including the Dirac equation, Klein-Gordon equation, semiclassical theory, quantum theory of the radiation field, and general electromagnetic fields. The text then takes a look at the covariant theory of radiation, as well as the relativistic quantum field theory, free electromagnetic field, electron and electromagnetic fields in interaction, and solution of the interacting field problem. The publication examines meson theory and nuclear forces and nuclear structure. Discussions focus on properties of the noninteracting system; characteristics of the two-body interaction; variational calculation of first-order energy; relativistic calculations in meson physics; and meson nucleon interactions. Hidden variables in the quantum theory and nuclear structure are also discussed. The selection is a valuable source of data for readers interested in quantum theory.