Contains notes for 32 lectures given by Richard Feynman at California Institute of Technology for a course from the 1959-1960 academic year. Lectures include: (1) Outline of the course. Review of principles of quantum mechanics. Superposition of amplitudes. (2) Spin and statistics. Degenercy. (3) Rotations and angular momentum. (4) Spin 1/2. Rules of composition of angular momentum. (5) Relativity. The positive and negative energy solutions. Waves propagating forward and backward in time. (6) Electromagnetic and Fermi couplings. (7) Fermi couplings and the failure of parity. Gravitation. Nuclear forces. Isotopic spin. The pion-nucleon coupling. (8) Pion-nucleon coupling (continued). Indirect interactions. (9) Strange particles. Associated production. K-mesons "strangeness". Baryons. Mesons. (10) Some consequences of strangeness. The decay of the neutral-kaon. (11) Strong coupling schemes. Fermi-Yang model. Global symmetry. Other models. (12) The decay of strange particles. Fermi coupling schemes. Proposed symmetry rules of the strangeness changing decays. (13) Strangeness changing decays (continued). The question of a universal coupling coefficient. (14) Comparison of the rules for strangeness changing decays with experiments. A summary of the salient features of the problem which we face. (15) An approach to the fundamental laws. Scalar particles. The transition probability. (16) Density of final states. Direct K to 2 decay and pi-K scattering. Rule for the propagation of a virtual meson. (17) The propagator for scalar particles. (18) The propagator in configuration space. Principle of least action. (19) Particles of spin 1. Photons. The principle of minimal electromagnetic coupling. Coupling and spin 0 particles with the electromagnetic field. The photon propagator. (20) The relation between virtual and real photons. Conservation of charge. Bremmstrahlung. (21) Problems: - - - and + - - scattering by photon exchange, Compton effect for -, + - - pair annihilation in flight. (22) Particles of spin 1/2. Infinitesimal operators for the general Lorentz transformation. The 2-component representation for zero mass. Co-spinors and contra-spinors. (23) Extension of finite mass. The Dirac equation. Probability current. The action principle, and the coupling of spin 1/2 particles with photons. (24) Properties of the 4-component spinor. The technique of spurs. (25) Compton effect for particles of spin 1/2. (26) Direct pair production by muons. (27) Higher order processes. Solution of the infrared catastrophe. The ultraviolet catastrophe. (28) Self-energy of the electron. Mass renormalization. The convergence factor. (29) Can we keep finite? The Lamb shift. The anomalous magnetic moment of the electron. Charge renormalization. (30) What is an external potential? Meson theory. (31) Theory of decay. Historical background. Invariant -decay couplings. Violation of parity and the two-component theory. Decay of a polarized neutron. (32) Properties of the -decay coupling. The -decay. The universal Fermi interaction. Fermi and Gamow-Teller contributions for non-relativistic nucleons. Summary of course.