As the principal legal organ of the United Nations, the International Court of Justice is a common source for practitioners and scholars looking for authoritative interpretations in international law. This holds true regarding questions relating to the regulation of the use of force by both the UN Charter and customary international law. This chapter describes the jurisprudence of the Court on the topic of the prohibition of the threat or use of force, including its customary nature, the right of self-defence, consent to the use of force, and States’ responsibility for use of force by non-State actors on their respective territories. Also considered is the Court’s use of its jurisprudence on the prohibition of the threat or use of force to interpret other obligations in international law, particularly in the context of US friendship, commerce and navigation treaties. Finally, this chapter discusses the Court’s role in preventing armed conflict in the first place, by providing States with a forum for the peaceful resolution of legal disputes.