Chronic disease has emerged in recent decades as the major cluster of health concerns of the American population. Increasing evidence indicates that, in most instances, these diseases have been present for long periods of time before becoming clinically manifest. In some instances, it is clear that they may begin in childhood and reach clinical expression only decades later. Furthermore, relevant risk factors for a number of these diseases have been identified and the beneficial effects of risk reduction defined. These disease characteristics translate into lengthy opportunities to identify, mitigate, or prevent serious chronic disorders. A useful framework invokes the health quantum, the “dose” of good health with which the individual is born and that is subjected to erosive forces at each stage of life from conception to old age. A coherent orientation toward the preservation of health across the lifespan is proposed, involving coordinated efforts by the individual, the clinical and public health communities, and the policy enterprise.