Within the context of the jus in bello component of the just war tradition, over the past century and a half the members of the international community have gradually developed a legal framework designed to limit the use of force in international and non- international armed conflicts. The purpose of this chapter is to examine the sources of that legal framework, which has in recent times come to be commonly known as international humanitarian law. The chapter first examines the principles that serve as the foundational source upon which international humanitarian law is based : military necessity, humanity, distinction, and proportionality. The chapter then delineates two of the other sources of international humanitarian law – conventional and customary international humanitarian law. These sources, combined with judicial opinions, the writings of various, recognized international legal authorities, and informed by the pioneering efforts by a variety of individual groups within the international community, collectively constitute the contemporary, synergistic, normative body of law designed to regulate the conduct of armed conflict across the spectrum of international and non-international violence.