International humanitarian law has developed through a pluralistic process. Its history reveals a pattern of rough proportionality between State opinio juris and non-State expressions of law. These diverse sources have maintained a respectable yet realistic balance between humanity and military necessity. However, current IHL dialogue presents a stark contrast to the vibrant and pluralistic exchanges of the past. The substantive input of non-State actors such as non-governmental organizations, tribunals, and scholars far outpaces the work of States. Parity of input, especially in quantitative terms, is surely too much to demand and surely not necessary given the special status of State opinio juris. However, States’ legal agencies and agents should be equipped, organized, and re-empowered to participate actively in the interpretation and development of IHL. This article, extracted from a larger work, argues that reinvigorating opinio juris would reestablish the pluralistic IHL dialogue that formerly tested, updated, and enriched the balance between military necessity and humanity.