International law has lacked a widely-accepted definition of armed conflict despite the essential human rights and other rules that depend on such a definition. During armed conflict, government forces have "combatant immunity" to kill without warning. They may detain enemy forces until the end of the conflict without the requirement to provide a speedy and fair trial. Governments may have asylum obligations or neutrality obligations based on the existence of armed conflict. To fill this gap in our knowledge of the law, the International Law Association's Committee on the Use of Force produced a report on the meaning of armed conflict. This book contains the report and papers delivered at an inter-disciplinary conference designed to inform the committee from a variety of perspectives.