Obesity causes serious medical complications and impairs quality of life. Moreover, in elderly persons, obesity can lead to frailty by exacerbating the decline in strength, endurance, balance and mobility associated with aging and physical inactivity. The primary objectives of the proposed research are to evaluate the independent and combined effects of weight loss and exercise on physical function, body composition, bone and muscle metabolism, and quality of life in frail, obese elderly men and women. The central hypothesis is that in frail obese elderly subjects, weight loss will improve physical function and quality of life, while the addition of exercise will not only augment improvement in these outcomes, but also attenuate the adverse effects of weight loss on bone and muscle masses. To test this hypothesis, 110 elderly (65-85 years old) obese men and women (body mass index [BMI] > 30 kg/m2) with physical frailty will be randomized to 4 treatment groups: 1) control, 2) 10% weight loss, 3) exercise training, and 4) 10% weight loss plus exercise training.