This course is an introduction to perturbative relativistic quantum field theory, for scalars, fermions, and gauge fields, in both the canonical and path integral formulations. The course begins with a review of relativistic wave equations. It introduces the Lagrangian formulation for classical fields and then discusses the canonical quantisation of free fields with spins 0, 1/2 and 1. An outline is given of perturbation theory for interacting fields and Feynman diagram methods for Quantum Electrodynamics are introduced. The course also introduces path integral methods in quantum field theory. This gives a better understanding of the quantisation of gauge theories and forms an essential tool for the understanding and development of the 'standard model' of particle physics. Topics include: Path integral formalism, Feynman rules, LSA formalism, loop diagrams and regularisation and renormalization of divergencies.