Due diligence is a prominent concept in international law, frequently referred to in arbitral awards, court decisions, and in scholarly discussions on state responsibility. However, until now, the specific normative content and systemic relation of due diligence to rules and principles of international law has largely remained unexplored. The present book provides a comprehensive analysis of the content, scope, and function of due diligence across various areas of international law, including international environmental law, international peace and security law, and international economic law. Sector by sector, contributors explore the diverse interactions between due diligence and area-specific substantive and procedural rules as well as general principles of international law. This book exposes the promises and limits of due diligence for enhancing accountability and compliance. It identifies the rise of due diligence as both a driver and signal of change in the international legal order towards risk management and proceduralisation.