In an era when premature death is relatively rare, people eventually show the well-known signs of ageing and are afflicted by one or more diseases of old age. How we fare depends on our genes and our life experience, but even if our genetic constitution promises long life we may be robbed of it by the strenuousness of our lifestyle or by misfortune. The signs of ageing reflect inexorable chemical change to important proteins acquired in childhood that never renew, making some kind of decay in old age inevitable. A major culprit responsible for this chemical damage, and probably the major risk factor for age-associated disease, is oxidative stress caused by “free-radicals” that leak from our mitochondria and other subcellular particles. Reduced calorie intake, exercise, and adequate intake of antioxidant vitamins and essential fatty acids all militate against free radicals and arguably might slow physical ageing. Ageing at a cellular level seems to be governed by a molecular clock that limits the number of divisions a cell makes in a lifetime, which may have a role in reducing the danger from potentially malignant cells. This process, too, may respond to free-radical damage.