The increasing prevalence of obesity in the United States and worldwide is a cause of great concern both for the health of individuals and for national health care systems. The underlying causes of the obesity epidemic are largely the product of what might be called "progress" in human civilization. These include increased availability of inexpensive food, urbanization, and technological advances that promote sedentary lifestyles. The combination of increased availability of food and lessened demand for physical activity combine to produce the progressive increase in body weight of individuals throughout the world. The public health consequences of these changes are enormous and pose a challenge to health policy at every level. A fundamental question has emerged: How do we approach the emerging epidemic ofobesity?