The Centers for Disease Control and Prevention (CDC) works for a future free of HIV/AIDS, viral hepatitis, sexually transmitted diseases (STDs), and tuberculosis (TB). Policy can have powerful effects on the complex, multisectoral factors that influence the population-level morbidity, mortality, and health disparities of these and other diseases.1-4 Public health policy approaches comprise laws, regulations, incentive systems, or other standardized procedures and practices aimed at influencing institutional and individual behavior to improve health and health equity.5,6 Laws and policies that were not designed to achieve health-related objectives also can have important, albeit unintended, health effects. A systematic study of the association between policies and population health is needed to guide the development and implementation of health-promoting policy strategies that are feasible and effective and that minimize harms. This supplemental issue of Public Health Reports provides timely research on policy interventions that have the potential to reduce the incidence, morbidity, or mortality of HIV/AIDS, viral hepatitis, STDs, and TB. Furthermore, the articles in this supplement demonstrate a typology of public health law and policy research that supports vital and comprehensive examination of the evidence on which policy interventions can be based. We summarize the proposed research typology, apply it to the diversity of articles included in this supplement, and discuss future directions for this important field of research.