Currently, one-third of children and two-thirds of adults in the United States are overweight or obese; this trend has persisted for the last decade and shows no sign of abatement.1- 2 Obesity tracks from childhood into adulthood, with unfolding and serious medical and economic consequences throughout the life course. One recent estimate suggests that if the current trend continues, obesity will account for more than $860 billion, or more than 16%, of health care expenditures in the United States by 2030.3 The need to find effective population-level obesity prevention strategies is among the most profound challenges in public health. Altering fundamental behaviors that govern energy balance is impossible when behaviors related to eating and physical activity are treated in isolation from the broader social, physical, economic, and policy context. Although energy consumption and energy expenditure may be at the core of the energy balance equation, obesity is, in fact, a medical manifestation of the complex interplay of biology and social change. However, the majority of research on obesity prevention has ignored larger changes in the social, physical, economic, and policy environments that doubtless are involved. Instead, most prevention efforts to date have focused on individually targeted strategies such as health education and behavioral skills training that turn out to be largely ineffective and unsustainable. The time is now ripe, and more urgent than ever, to implement a new, multilevel approach to understanding the basis of the obesity epidemic and how to reverse it.