The Handbook of International Humanitarian Law sets out a black letter text of international humanitarian law accompanied by case analysis and extensive explanatory commentary by a team of distinguished and internationally renowned experts. This is the fourth edition of this influential and comprehensive handbook. It has been extensively updated and revised, taking into account recent legal developments, such as the 2017 Nuclear Weapons Prohibition Treaty, as well as the ongoing debate on many old and new issues. Areas covered by the book include the notion of direct participation in hostilities; air and missile warfare; military operations in outer space; military cyber operations; belligerent occupation; operational detention; and the protection of the environment in relation to armed conflict. The continuing need to consider borderline issues of the law of armed conflict as well as the interplay of international humanitarian law, human rights law, and other branches of international law is highlighted. This Handbook provides an in-depth understanding of the development and current problems of the law of armed conflicts. It considers legal and policy issues both from the views of academics and military and diplomatic practitioners. Finally - and most importantly - it offers a complete account of activities that should be taken to improve the implementation and enforcement of international humanitarian law.