Many legal scholars have characterized the international community’s “responsibility to protect” as a moral or political ideal without a well-established foundation in international law. In this chapter, I argue that the legal character of the responsibility to protect cannot be so easily dismissed. The idea that individual states and the broader international community share responsibility for guaranteeing the security and basic rights of human beings can be traced back to international law’s colonial-era origins, a time when Western nations rationalized their subjugation of indigenous peoples by casting themselves as benevolent “guardians” or “trustees” for humanity. Although the historical record suggests that colonial powers abused fiduciary rhetoric as a pretext for subjugating, exploiting, and even destroying indigenous communities, over time the continuing penetration and diffusion of fiduciary concepts has subtly redefined sovereignty itself as a form of legal authority that is entrusted to states as fiduciaries for the benefit of humanity. Under this fiduciary model of sovereignty, international law and international institutions are necessary to mediate the relationship between states and their people, ensuring that this relationship is not corrupted by domination or instrumentalization. When states flagrantly neglect their responsibility to protect their people from abuse or affirmatively violate the human rights of their people, international law entrusts the international community as a whole — acting primarily through the U.N. Security Council — with responsibility to intercede for the protection of oppressed peoples. Although the international community’s responsibility to protect requires further institutional development, it constitutes an essential feature of international legal order.