The main object in writing this book has been to present the subject of elementary particle physics at a level suitable for advanced physics undergraduates or to serve as an introductory text for graduate students.

Since the first edition of this book was produced over 25 years ago, and the third edition over 10 years ago, there have been many revolutionary developments in the subject, and this has necessitated a complete rewriting of the text in order to reflect these changes in direction and emphasis. In comparison with the third edition, the main changes have been in the removal of much of the material on hadron–hadron interactions as well as most of the mathematical appendices, and the inclusion of much more detail on the experimental verification of the Standard Model of particle physics, with emphasis on the basic quark and lepton interactions. Although much of the material is presented from the viewpoint of the Standard Model, one extra chapter has been devoted to physics outside of the Standard Model and another to the role of particle physics in cosmology and astrophysics.

Many – indeed most – texts on this subject place particular emphasis on the power and beauty of the theoretical description of high energy processes. However, progress in this field has in fact depended crucially on the close interplay of theory and experiment. Theoretical predictions have challenged the ingenuity of experimentalists to confirm or refute them, and equally there have been long periods when unexpected experimental discoveries have challenged our theoretical description of high energy phenomena.