Healthy ageing is the ideal trajectory from birth to death. As we reach older age, physical changes are inevitable, but it is not simply the effect of these changes that makes ageing healthy or unhealthy. An older person may have many years of incapacity as they decline slowly towards death. Or they may be well and functioning happily until a very rapid shift into loss of life (the ideal of dying suddenly in one’s sleep while in the midst of life). It is the latter trajectory that many people desire and the aim of promoters of healthy ageing. However, the question raised by this recognition of the ideal trajectory is, what is health?