For as long as human beings have thought about their bodies, it has been recognized that exposure to noxious physical, mental, and emotional experiences has negative effects on health. There exist, for example, classic literary descriptions of the way in which personal tragedy can “age” individuals and destroy their physical wellbeing. It has only been in the last half-century, however, that an attempt has been made to deal with this phenomenon scientifically. The result has been a bewildering and rapidly increasing literature dealing with “stress” in humans and animals.