Basic research on aging has moved well beyond describing the aging of physiological systems and developing theories of aging, to the pursuit of mechanistic answers to questions such as: Why do we age? Why do individuals within a population age differently? Why do different species have such different life spans? How do aging changes increase the risk of developing age-related disease? and Can we develop safe and effective interventions to reduce age-related disability? Two general areas of research promise to provide answers to these questions. One is the attempt to understand the mechanisms by which caloric restriction extends longevity and delays the onset of age-related disease. The other is the identification of genes which strongly influence the rate of aging in various animal model systems. Recent results in the latter area of research are providing new insights into the answers to these central aging questions and may help us understand how caloric restriction retards aging.