This book analyses the origins of security dilemmas in the South China Sea (SCS) and the significance of China’s actions in asserting its claim from the perspective of defensive realist theory. In its analysis, the book argues that security dilemmas in the SCS first arose between China and other SCS claimants, and then between China and the United States. Research in this book provides significant support to the defensive realist theory vis-à-vis offensive realism. It encourages adopting a reassurance policy to reach a peaceful resolution to the SCS disputes between China, the other claimants, and the United States. The book will be useful for policymakers, academics, researchers and students.