Why do law reforms spread around the world in waves? In the dominant account of diffusion through technocracy, international networks of elites develop orthodox policy solutions and transplant these across countries without regard for the wishes of ordinary citizens. But this account overlooks a critical factor: in democracies, reforms must win the support of politicians, voters, and interest groups. This book claims that laws spread across countries in very public and politicized ways, and develops a theory of diffusion through democracy. I argue that politicians choose to follow certain international models to win domestic elections, and to persuade skeptical voters that their ideas are not radical, ill-thought-out experiments, but mainstream, tried-and-true solutions. This book shows how international models generated domestic support for health, family, and employment law reforms across rich democracies. Information that international organizations have endorsed certain reforms or that foreign countries have adopted them is valuable to voters. Public opinion experiments show that even Americans respond positively to this information. Case studies of election campaigns and legislative debates demonstrate that politicians with diverse ideologies reference international models strategically, and focus on the few international organizations and countries familiar to voters. Data on policy adoption from many rich democracies document that governments follow international organization templates and imitate the policy choices of countries heavily covered in national media and familiar to voters. The book provides a direct defense to a major criticism international organizations and networks face: that they conflict with domestic democracy. The book also explains how to design international institutions and transnational advocacy campaigns to spread laws more effectively. The introductory chapter follows.