This book is the definitive tutorial text and reference work on free electron lasers. Since the publication of the first edition in 1992 there has been a significant increase both in the number of free-electron lasers in use worldwide, and in the understanding of the various regimes for these devices. In order to maintain the position of this book as the most comprehensive and thorough reference and tutorial in the field, the authors have completely updated the book. In addition to updates and corrections to chapters in the first edition, new chapters have been added.