In anaesthetist Dr Kevin Fong's television programmes he has often demonstrated the impact of extremes on the human body by using his own body as a 'guinea pig'. So Dr Fong is well placed to share his experience of the sheer audacity of medical practice at extreme physiological limits, where human life is balanced on a knife edge. Through gripping accounts of extraordinary events and pioneering medicine, Dr Fong explores how our body responds when tested by the extremes of heat and cold, vacuum and altitude, age and disease. He shows how science, technology and medicine have taken what was once lethal in the world and made it survivable. This is not only a book about medicine, but also about exploration in its broadest sense - and about how, by probing the very limits of our biology, we may ultimately return with a better appreciation of how our bodies work, of what life is, and what it means to be human.