Using McKinlay's population model of prevention, this series assesses the current state of the art for six lifestyle behaviors: tobacco use, alcohol abuse, drug abuse, unhealthy diet, sedentary lifestyle, and risky sexual practices related to human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). More progress has been made in "downstream" individually oriented treatments than in broader, more environmentally focused interventions. Promising trends include: a shift toward lower cost minimal-contact and self-help "downstream" programs; the development of tailored messages and stage-based "midstream" initiatives that can reach everyone in a defined population or setting; and the emergence of "upstream" policy advocacy strategies. Improving the power and reach of health behavior change will require advances in biobehavioral research to develop more powerful behavior change strategies along with efforts to more widely disseminate the effective interventions that already exist. Growing evidence supports McKinlay's premise that full-spectrum (downstream to upstream) interventions are needed for greatest population impact. Progress also will depend on finding new ways to address the needs of special populations--including underserved low-income groups, racial and ethnic minorities, individuals with multiple risk behaviors, and youth and their families.