Article 51 United Nations Charter

Article 51 of the United Nations Charter is under Chapter VII: Action with Respect to Threats to the Peace, Breaches of the Peace, and Acts of Aggression

Article 51

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.

See also: Article 50 United Nations Charter