This book introduces the basic framework, principles, and new trends of international cooperation in criminal justice, and also shows examples of actual cases on this issue, some successful, some not. Based on decades of experience as prosecutors of international crimes, the book proposes new ways of international cooperation which could result in more effective countermeasures to international crimes beyond the traditional methods. The best way to fight against transnational crimes is international cooperation between the law enforcement agencies of each country. For close and friendly cooperation, it is recommendable to lower the barriers of sovereignty of each nation. We have to lower the fences of boundary and open a side door of friendship with neighbors. This is the new initiative on international cooperation in criminal justice. It is also a way to achieve direct contact and speedy response between law enforcement agencies. While criminals take advantage of globalization and emerging technologies to commit a diverse range of crimes across the borders, law enforcement against transnational crime takes a very long time. It could take months to obtain even a copy of a necessary document or perhaps years to have the fled criminals extradited. Facing this reality, authors of this book suggest an innovative and viable approach to the international cooperation on new concept, direct contact and speedy response between law enforcement agencies worldwide. Accessible, detailed, and practical, this book will provide valuable references of practices in international criminal law and work as a practical guide to the lawyers, law enforcement agents, law students, and law professionals in the international legal circle.