In the past few years a course in relativistic quantum fields, which is the basic quantum theory of matter, has become established as a requirement for university students of physics. This book is conceived as a textbook for beginning students of the subject. The plan is that of the first half of the authors’ monograph “Introduction to quantum field theory” (Russian), 3rd ed., Nauka, Moscow (1976); English translation Wiley, New York (1980) and contains a linear presentation of the theory of quantum fields, beginning with free classical models and ending with procedures for eliminating divergence in perturbation theory. The presentation is highly simplified in comparison with the above monograph. The material of each section corresponds to about a one-and-one-half hour lecture, and the book as a whole to a full-year course. The technical material relegated to the Appendix and the sets of problems and exercises found in seven assignments at the end of the book are intended for seminar study. For an English translation of the first ed., see Benjamin/Cummings Publ. Co., Reading (1983).