This textbook is aimed at biochemical and medical graduates and beyond and builds upon the first edition, published in 2014, with the addition of several new chapters reflecting updates in the field. It would be of particular value to those wanting to understand the clinical applications of gene therapy. The chapters are divided into four parts. Part I provides an introduction of basic principles including useful discussions around the history of gene therapy and the principles of different genetic modification strategies. Part II focuses on vectors and gene delivery techniques including viral and non-viral strategies. Part III then moves towards the therapeutic applications of gene therapy discussing cancer gene therapy, immunodeficiencies and neurological disease and contains the main updates from the first edition. New chapters included here are focused on CAR-T cells and their use in cancer immunotherapy, therapies for severe combined immunodeficiencies (SCID) and cystic fibrosis. Finally, part IV focuses on vector production and safety. The volume of information covered in this book is reflected in the heavy word count. Those looking for succinct phrasing and lots of diagrams may find this level of information difficult to process; however, those willing to work their way through the text will find interesting discussions about different applications and thus can improve their technical knowledge.