The federal government has unsurpassed resources and the authority to promote public health through law. In some domains, like pharmaceuticals, federal law creates uniformity. In others, like emergency preparedness or disease control, federal law helps coordinate and support state measures. Congress can use the power of its purse to encourage states to adopt effective laws. Federal agencies enforce a wide range of health and safety rules alone and in cooperation with state and local officials. Research is essential to guide these efforts by showing what laws and enforcement practices are effective.