Throughout the world, populations are ageing. The response of the health services needs to be based on a knowledge of the nature of human ageing and the principles of rational health care for older people. Ageing comes about from interactions between intrinsic (genetic) and extrinsic (environment and lifestyle) factors. Health care has to be responsive to the general needs of older people, but also to recognize the heterogeneity produced by different rates and patterns of individual ageing. There are now real possibilities of improving the course of human ageing through modulation of both intrinsic and extrinsic processes. There is also a need to adapt social institutions to what is a permanent change in demography.