This is now the third edition of a text that is already well established as one of the standard undergraduate books on the subject of elementary particle physics. Professor Hughes has updated the whole text in line with current particle nomenclature and has added material to cover important new developments. There is also a completely new major chapter on particle physics and cosmology, an exciting subject which has become an area of increasing importance in recent years. In this field much can be learnt from the way the subject developed, and so, where this helps its understanding, an historical treatment is used. At all stages the theoretical development is closely linked to the relevant experimental measurements, providing a sound foundation to what might otherwise appear as a rather abstract subject. This book will fill the need for an introductory undergraduate textbook aimed at students taking a first course in this fascinating area of modern physics.