An Institute of Medicine committee was convened to explore the links between biological, psychosocial, and behavioral factors and health and to review effective applications of behavioral interventions. Based on the evidence about interactions of the physiological responses to stress, behavioral choices, and social influences, the committee encouraged additional research efforts to explore the integration of these variables and to evaluate their mechanisms. An understanding of the social factors influencing behavior is growing and should be considered in programs and policies for public health, in addition to individual behavior and physiological status. Interventions to change behaviors have been directed toward individuals, communities, and society. Many intervention trials have documented the capacity of interventions to modify risk factors. However, more trials that include measures of morbidity and mortality to determine if the strategy has the desired health effects are needed. Behavior can be changed and new behaviors can be taught. Maintaining behavior changes is a greater challenge. Although short-term changes in behavior following interventions are encouraging, long-duration efforts are needed to improve health outcomes and to provide long-term assessments of effectiveness. Interventions aimed at any level can influence behavior change; however, existing research suggests that concurrent interventions at multiple levels are most likely to sustain behavior change and should be encouraged.