The permanent five (P5) members of the United Nations Security Council have a firm duty to prevent genocide in light of the due diligence standard under conventional, customary, and peremptory international law. This perceptive book explores the positive obligations of these states to act both within and without the Security Council context to prevent or suppress imminent or ongoing genocide. The author successfully argues why the duty to prevent genocide is not only a customary, but also an absolute norm of international law, and analyses the scope of the due diligence standard regarding the duty to prevent genocide. In doing so, he considers the ramifications of this on the actions of the P5 members of the Security Council, both inside and outside of this eminent body. Significantly, Heieck proposes a legal test for identifying jus cogens norms, and explores the effect of these on the actions and omissions of specifically identified members of the United Nations (UN). Topical and insightful, A Duty to Prevent Genocide will be an important read for both academics and students of international law and politics who wish to further understand the legal nature of the duty of the P5 members to prevent genocide. It will also provide valuable insights for policy makers of the P5 Member States.