This book does not pretend to give an overview of this complex subject. Instead experts in the field are given the opportunity to give their personal perspective on chosen aspects of the topic. This is valuable; however, it probably makes the book more relevant to the insider than to a general reader with an interest in this topic. The quality of the science is high and the chapters by Barron & Manson (Gene targeting) and Williamson (Immunotherapy) are models of clarity. The latter alone justifies this book's existence. Unfortunately, many of the chapters are organized by technology used (cell culture, transgenesis, etc.), rather than scientific questions being addressed. Whether or not this book is currently definitive or how long it might remain relevant in such a fast moving field are open questions. It is, however, a useful stepping-stone and should be read as such by those working in this field.