The book attempts to provide an introduction to quantum field theory emphasizing conceptual issues frequently neglected in more 'utilitarian' treatments of the subject. The book is divided into four parts, entitled respectively 'Origins', 'Dynamics', 'Symmetries', and 'Scales'. The emphasis is conceptual - the aim is to build the theory up systematically from some clearly stated foundational concepts - and therefore to a large extent anti-historical, but two historical Chapters ('Origins') are included to situate quantum field theory in the larger context of modern physical theories. The three remaining sections of the book follow a step by step reconstruction of this framework beginning with just a few basic assumptions: relativistic invariance, the basic principles of quantum mechanics, and the prohibition of physical action at a distance embodied in the clustering principle. The ``Dynamics' section of the book lays out the basic structure of quantum field theory arising from the sequential insertion of quantum-mechanical, r...show more