W. French Anderson, M.D. The publication of this book comes at an opportune time for the young field of human gene therapy. After a decade of long struggle at the laboratory bench and many long hours under the harsh lights of the federal review process, gene therapy has emerged as a legitimate scientific discipline. It is now time to move away from the period of questioning whether gene therapy will be a useful part of the physician armamentarium to begin to actively teach the concepts and practices that make gene therapy a reality. This book is a comprehensive collection of chapters that describe the basic biology and potential application of viruses as gene transfer reagents. It is not a coincidence that a modified virus was the reagent used in the first human gene therapy trials. Viruses have evolved with the human species (and most likely with all forms of life) to be the masters of gene transfer.