Synchrotron radiation sources are now used routinely by thousands of research scientists and engineers throughout the world to perform experiments in biology, physics, materials science, chemistry and so on. The very best of these sources are based upon the use of undulator and wigglerinsertion devices that can enhance the intensity of the radiation by many orders of magnitude. This book, which is part of the Oxford Series on Synchrotron Radiation, brings together both a detailed step by step description of the radiation properties from these devices as well as an explanation ofthe practical realisation of actual devices using available magnet technologies. The book is aimed at not just the users but also the providers of synchrotron radiation. It takes the reader through the fundamental issues, and provides sufficient depth so as to be an indispensible reference to lightsource designers, accelerator physicists and insertion device specialists. The approach taken is to provide the reader with all of the essential information and to back this up with practical examples and illustrations wherever possible.