Public debates in the language of international law have occurred across the 20th and 21st centuries and have produced a popular form of international law that matters for international practice. This book analyses the people who used international law and how they used it in debates over Australia's participation in the 2003 Iraq War, the Vietnam War and the First World War. It examines texts such as newspapers, parliamentary debates, public protests and other expressions of public opinion. It argues that these interventions produced a form of international law that shares a vocabulary and grammar with the expert forms of that language and distinct competences in order to be persuasive. This longer history also illustrates a move from the use of international legal language as part of collective justifications to the use of international law as an autonomous justification for state action.