With the rapidly expanding population of old people in every affluent country, important new social problems are emerging. It is natural, therefore, that gerontology is attracting many of the academically minded, and within the medical profession a fully fledged speciality of geriatrics is growing up. With age every bodily system becomes less efficient and more vulnerable, though in some the effect is more striking than in others. Anyone interested in almost any aspect of human biology will find that some facet of ageing is relevant to his field of study. Immunologists are no exception and in any recent discussion on theories of ageing the auto-immune or immunological approach will be found mentioned. It is characteristic of theorizing in any difficult biological area not susceptible to effective experimental study that the three formulations of immunological approaches to ageing, by Walford, Burch, and myself, have not very much in common. There is a great deal more to ageing than the development of low-grade auto-immune disease, but this is part of the story and it would be inappropriate to omit the topic in a book on general aspects of auto-immunity.