Abstract: Can we say, definitively, when an armed conflict no longer exists under international law? The short, unsatisfying answer is sometimes: it is clear when some conflicts terminate as a matter of international law, but a decisive determination eludes many others. The lack of fully-settled guidance often matters significantly. That is because international law tolerates, for the most part, far less violent harm, devastation, and suppression in situations other than armed conflicts. Thus, certain measures governed by the laws and customs of war — including killing and capturing the enemy, destroying and seizing enemy property, and occupying foreign territory, all on a possibly large scale — would usually constitute grave violations of peacetime law. This Legal Briefing details the legal considerations and analyzes the implications of that lack of settled guidance. It delves into the myriad (and often-inconsistent) provisions in treaty law, customary law, and relevant jurisprudence that purport to govern the end of war. Alongside the doctrinal analysis, this Briefing considers the changing concept of war and of what constitutes its end; evaluates diverse interests at stake in the continuation or close of conflict; and contextualizes the essentially political work of those who design the law. In all, this Legal Briefing reveals that international law, as it now stands, provides insufficient guidance to precisely discern the end of many armed conflicts as a factual matter (when has the war ended?), as a normative matter (when should the war end?), and as a legal matter (when does the international-legal framework of armed conflict cease to apply in relation to the war?). The current plurality of legal concepts of armed conflict, the sparsity of IHL provisions that instruct the end of application, and the inconsistency among such provisions thwart uniform regulation and frustrate the formulation of a comprehensive notion of when wars can, should, and do end. Fleshing out the criteria for the end of war is a considerable challenge. Clearly, many of the problems identified in this Briefing are first and foremost strategic and political. Yet, as part of a broader effort to strengthen international law’s claim to guide behavior in relation to war and protect affected populations, international lawyers must address the current confusion and inconsistencies that so often surround the end of armed conflict.