The high and still increasing prevalence of obesity in US children, adolescents, and adults poses a major economic and health threat to our society. The three reviews in this minisymposium on obesity explore the health issues by: 1) describing the public health impact of obesity; 2) examining the multiple and complex environmental influences on eating and physical activity patterns; and 3) considering how the development of obesity during childhood and adolescence can be prevented through interventions in school, family, and primary care settings. This overview explains the importance, for effective long-term obesity prevention and control, of intersectoral policy and environmental initiatives-in addition to behavior change approaches aimed at individuals. The need for public health professionals to influence and operate within a variety of non-health sectors such as transportation, education, urban planning, and commerce may be seen as the greatest barrier but may also be the greatest opportunity.