The original edition comprised two books, labelled part 1 and part 2. The first covered general aspects of relativistic quantum mechanics and relativistic quantum field theory, leading onto quantum electrodynamics. The second continued with quantum electrodynamics and what was then known about the strong and weak interactions. These books were published in the early 1970s, at a time when the strong and weak forces were still not well understood. In the second edition, the corresponding sections were scrapped and replaced with more topics in the well-established quantum electrodynamics, and the two parts were unified into one, thus providing a one-volume exposition on relativistic quantum field theory with the electromagnetic interaction as the prototype of a quantum field theory.