This book is a pedagogical introduction to quantum field theory, suitable for a students' first exposure to the subject. It assumes a minimal amount of technical background and it is intended to be accessible to a wide audience including students of theoretical and experimental high energy physics, condensed matter, optical, atomic, nuclear and gravitational physics and astrophysics. It includes a thorough development of second quantization and the field theoretic approach to nonrelativistic many-body physics as a step in developing a broad-based working knowledge of the basic aspects of quantum field theory.  It presents a logical and systematic first principles development of relativistic field theory and of functional techniques and perturbation theory with Feynman diagrams, renormalization, and basic computations in quantum electrodynamics.