This introductory chapter discusses societies that have deliberately undertaken a program of demilitarization, with deep consequences in public and political culture as well as statecraft. The developments have occurred in decades dominated by the arms races of the Cold War and the assumption of most governments that the logics of success and security called for more weapons. Exploring the history of explicit demilitarization raises two related issues, both of which provide context for future studies. First, demilitarization as a term can be validly applied to a number of patterns of change—there is no heroic single definition. Second, while contemporary demilitarization has some distinctive features, it links with and builds on earlier historical precedents of several types.