Book excerpt: Behavioral science is playing an increasing role in public policy, and it is raising new questions about fundamental issues - the role of government, freedom of choice, paternalism, and human welfare. In diverse nations, public officials are using behavioral findings to combat serious problems - poverty, air pollution, highway safety, COVID-19, discrimination, employment, climate change, and occupational health. Exploring theory and practice, this Element attempts to provide one-stop shopping for those who are new to the area and for those who are familiar with it. With reference to nudges, taxes, mandates, and bans, it offers concrete examples of behaviorally informed policies. It also engages the fundamental questions, include the proper analysis of human welfare in light of behavioral findings. It offers a plea for respecting freedom of choice - so long as people's choices are adequately informed and free from behavioral biases.