Extensively classroom-tested, A Course in Field Theory provides material for an introductory course for advanced undergraduate and graduate students in physics. Based on the author's course that he has been teaching for more than 20 years, the text presents complete and detailed coverage of the core ideas and theories in quantum field theory. It is ideal for particle physics courses as well as a supplementary text for courses on the Standard Model and applied quantum physics. The text gives students working knowledge and an understanding of the theory of particles and fields, with a description of the Standard Model toward the end. It explains how Feynman rules are derived from first principles, an essential ingredient of any field theory course. With the path integral approach, this is feasible. Nevertheless, it is equally essential that students learn how to use these rules. This is why the problems form an integral part of this book, providing students with the hands-on experience they need to become proficient. Taking a concise, practical approach, the book covers core topics in an accessible manner. The author focuses on the basics, offering a balanced mix of topics and rigor for intermediate physics students.