Internationally recognized scientists, clinicians, and technologists review and explain the fundamental molecular and cellular biology that has been applied to the emerging field of transplant immunology and xenotransplantation, and what impact these advances might optimally have on medicine and science. The authoritative experts writing here-many of whom made the basic discoveries underlying the recent advances-examine the biological and immunological hurdles to xenotransplantation, illuminating how the immune system interacts with the xenograft and laying a practical foundation for the use of genetic engineering and animal transplants in the treatment of human disease.