During the twentieth century, development emerged as a concept and an organized activity in international society. Every year, governments, international organizations, and private foundations send money and experts abroad to promote economic growth and social development. This collection of essays by a group of prominent historians provides the best portrait yet of the origins and evolution of international development. The rise of Cold War–era modernization theory and the geopolitics of U.S. foreign aid are well-known stories. But these authors show that international development has a much longer history, one that is intertwined with the emergence of the modern global order. In her contribution, Amanda Kay McVety traces the concept to the Enlightenment and the work of early political economists, such as Adam Smith. Others look at how development was entangled with nineteenth-century European empires and twentieth-century struggles over decolonization and nation building. A chapter by Manela charts the history of disease control and the emergence of a global institutional framework for development assistance. Timothy Nunan explores the efforts of European foresters, American nongovernmental organizations, and Soviet engineers to develop Afghanistan in the 1960s and 1970s. Taken together, these and other contributions suggest that international development is best understood not as the diffusion of knowledge from the West to the rest or as a manifestation of the Cold War struggle but instead as a shared language and set of practices that transcend ideological and political divides.