From the Preface: "From the 1950s until 1968, the theory of finite groups underwent an intense period of growth, including the first major classification theorem concerning simple groups as well as the construction of the first new sporadic simple group in a hundred years. In writing this book, my aim was to describe that development in sufficient detail for the interested reader to reach the frontiers of the subject and thereby participate in the excitement that then surrounded the study of simple groups ... In the intervening ten years [since the first edition of this work], an equally dramatic change has occurred ... a complete classification of the finite simple groups has now almost approached a reality ... Literally thousands of journal pages have been devoted to their study and powerful new techniques have been developed ... In most instances, these developments constitute a continuation rather than a replacement of the material in this book."