The overall purpose of this book is to expose the reader/student to a comprehensive and detailed, yet still easily accessible, overview of the whole field of gene therapy, ranging from vector development and therapeutic gene selection to the results of the most recent clinical trials.The language is plain and, whenever possible, non-technical. Since the book is intended to be a textbook in the field of gene therapy in both the basic science and clinical areas, when technical descriptions are required, they are provided either in the main text or in add-on explanatory boxes. For example, clinical readers might find it difficult to understand the principles of viral vector design without knowing some molecular details of viral genome organization and virus life cycle, and basic scientists might be unaware of the clinical and therapeutic advancements for the various disorders treated by the book. In these cases, basic explanations are provided.In this respect, it is worth pointing out that the book is truly a gene 'therapy' book; it only considers conditions and experimental approaches based on gene transfer that have already proceeded to the clinic or are close to doing so. Basic research on gene transfer or nucleic acid modification is only presented if it is when close to clinical application. Following the same principle, only diseases for which clinical trials have already been performed or are planned are considered, or those for which solid and encouraging pre-clinical, animal experimentation results are available.