The intent of this book is to bridge the link between experimental obser­ vations and theoretical principles in accelerator physics. The methods and concepts, taken primarily from high energy accelerators, have for the most part already been presented in internal reports and proceedings of accelera­ tor conferences, a portion of which has appeared in refereed journals. In this book we have tried to coherently organize this material so as to be useful to designers and operators in the commissioning and operation of particle accelerators. A point of emphasis has been to provide, wherever possible, experimental data to illustrate the particular concept under discussion. Of the data presented, most are collected from presently existing or past accelerators and we regret the problem of providing original data some of which appear in less accessible publications - for possible omissions we apologize. Regarding the uniformity of the text, particularly with respect to symbol definitions, wehave taken the liberty to edit certain representations of the data while trying to maintain the essence of the presented observations. Throughout the text we have attempted to provide references which are readily available for the reader.