The crime of rape has been prevalent in all contexts, whether committed during armed conflict or in peacetime, and has largely been characterised by a culture of impunity. International law, through its branches of international human rights law, international humanitarian law and international criminal law, has increasingly condemned such violence and is progressively obliging states to prevent rape, whether committed by a state agent or a private actor. Whereas the prohibition of rape has been consistently recognised in these areas of law, the definition of the offence has been a later concern to international law. Attempts to define the crime have, however, been made by the ad hoc tribunals (International Criminal Tribunal for Rwanda and the International Criminal Tribunal for the former Yugoslavia), regional human rights courts and UN treaty bodies. Increasing duties are thus placed on states, not only to prevent rape through the enactment of criminal laws, but to adopt specific elements of the crime in domestic legislation. This study systematises and analyses such emerging obligations in international law. This leads to overarching questions on the fragmentation and harmonisation of norms between various regimes in international law.