Because war can be unnecessarily inhumane, a series of agreements and treaties have established principles of how to conduct war legitimately, treat prisoners humanely, and even how one country can occupy another militarily within the framework of international law. After an extensive history of the concept of “just war” and the development of war crimes over centuries, a list is provided of 639 offenses that fall into four categories—illegality of war, crimes in the conduct of war, mistreatment of prisoners captured in war, and mismanagement of a militarily occupied country. Although war illegality is discussed at some length, with examples, the other war crimes are enumerated by category and subcategory. No comprehensive list of war crimes has ever been published before. The operational code of how to prosecute war criminals is provided.