This book is aimed primarily at the reader who wishes either to do theoretical research in elementary particle physics, or to be able to follow theoretical papers dealing with this subject. It should be suitable for graduate students who have a good grounding in quantum mechanics and should provide such students with a background which will enable them to read the current literature in elementary particle theory and to undertake research projects in this field. At the same time we hope that it will be useful as a source book to practising theorists, and also that it will be of value to experimentalists who wish to acquire the basic theoretical techniques.