Lecture, four hours. Requisite: course 221C or equivalent and knowledge of basic special relativity. Introduction to relativistic quantum field theory starting from first principles. Topics include particles as unitary representations of Poincare group; fields as finite-dimensional representations of Lorentz group; discrete space-time symmetries; quantization of free scalar, spinor, and gauge fields; Casimir effect; classical interacting scalar, spinor, and gauge fields; and LSZ formalism for calculation of S-matrix from quantum field theory correlators. S/U or letter grading.