Overweight and obesity are important determinants of population health. Prevention of weight gain is dependent on the successful balancing of eating and physical activity behaviors. Planned promotion of healthful behavior requires insights into important and changeable determinants and correlates of behavior change. The modest effects of health education have induced a shift in focus from personal to environmental correlates of eating and physical activity behaviors. Six systematic reviews were conducted in 2005 of observational studies of environmental correlates and environmental interventions for weight-related eating behaviors and physical activity for children, adolescents, and adults. The reviews of 297 observational studies showed that few investigations of environmental associations have been replicated, and that most studies used weak research designs and nonvalidated self-report measures, were restricted to micro-environmental factors, and failed to apply multilevel analyses. There is, therefore, very little evidence for an association between environmental factors and weight-related behaviors. However, the reviews of 112 intervention studies indicated much stronger evidence for positive effects of micro-physical and sociocultural environmental changes on eating and physical activity behaviors. Inspired by quotes from Kurt Lewin, we argue that before large-scale environmental change interventions are launched, better-designed and -conducted research on the true importance of environmental factors, including macrolevel factors, for obesogenic behavioral change is needed. Such research should (1) develop better measures of environmental exposure, (2) attempt to integrate personal and environmental correlates of obesogenic behaviors, (3) take a solution-oriented, rather then a problem-oriented approach, and (4) identify access points for inducing behavior change instead of finding explanations for existing behavioral patterns.