This book examines the development of same-sex unions policy (SSU) in eighteen western democracies and seeks to explain why the overwhelming majority of these countries have implemented a national law to recognise gay and lesbian couples since 1989. The author argues that this dramatic wave of SSU policy adoptions across Western Europe and North America is, to a significant degree, the product of international norm diffusion and socialisation. The first part of the study traces the creation of a norm for relationship recognition within the European polity, and describes how this norm has...