Calorie restriction (CR) is the only paradigm that has consistently increased lifespan in a wide variety of model organisms. Many hypotheses have been proposed as the underlying mechanism, including a reduction in body size and adiposity, which is commonly observed in calorie-restricted animals. This has led to investigations as to whether similar changes in body composition produced by increasing energy expenditure via exercise can replace or enhance the benefits of reducing energy intake. The goal of this chapter is to review and discuss the evidence regarding exercise as a CR mimetic for healthy aging and longevity. In rodents, the data clearly show that exercise, regardless of body weight changes, can improve health and survival, but unlike CR, fails to extend lifespan. In humans, short-term weight loss studies show that exercise and CR produce similar improvements in disease risk factors and biomarkers of aging, while some parameters clearly benefit more with exercise. Epidemiologic evidence in humans supports exercise as a strategy to reduce the risk of morbidity and mortality, but not to extend lifespan. It is unknown whether CR can extend human lifespan, but the metabolic profile of humans engaged in long-term CR shares many similarities with calorie restricted rodents and nonhuman primates. In conclusion, like CR, exercise can limit weight gain and adiposity, but only CR can extend lifespan. Therefore, in rodents, the ability of CR to slow aging is apparently more dependent on decreasing nutrient flux, rather than changes in energy balance and body composition.