The objectives of this book are twofold. First, it provides an accessible introduction to the vast literature dedicated to the study of public opinion. Examining how its influence on diplomacy has been increasingly acknowledged, the book will show how public opinion has been embraced as a legitimate subject for scrutiny by international historians. Second, the book explores five case studies, looking at the role of public opinion in shaping British policy at the Paris Peace Conference, French policy in the era of 1930s appeasement, the policy choices of the United States during the Vietnam War, global responses to apartheid-era South Africa, and public attitudes across the EU regarding European integration. This closer examination incorporates different methodological approaches - old and new - to the complex task of ascertaining the impact of public opinion on the 'high' politics of diplomacy. The book thus provides students and scholars alike with a 'state of the field' overview, demonstrating both the vibrancy of public opinion research to date and the possibilities for exciting new directions in the future.