International humanitarian law is the branch of customary and treaty-based international positive law whose purposes are to limit the methods and means of warfare and to protect the victims of armed conflicts. Grave breaches of its rules constitute war crimes for which individuals may be held directly accountable and which it is up to sovereign states to prosecute. However, should a state not wish to, or not be in a position to, prosecute, the crimes can be tried by international criminal tribunals instituted by treaty or by binding decision of the United Nations Security Council. This brief description of the current legal and political situation reflects the state of the law at the dawn of the twenty-first century. It does not, however, describe the work of a single day or the fruit of a single endeavour. Quite the contrary, it is the outcome of the international community’s growing awareness, in the face of the horrors of war and the indescribable suffering inflicted on humanity throughout the ages, that there must be limits to violence and that those limits must be established by the law and those responsible punished so as to discourage future perpetrators from exceeding them.