The Charter of the United Nations (also known as the UN Charter) is the foundational treaty of the United Nations, an intergovernmental organization. Consisting of a preamble and 19 chapters divided into 111 articles, it establishes the purposes, governing structure, and overall framework of the UN system, including its six principal organs: the Secretariat, the General Assembly, the Security Council, the Economic and Social Council, the International Court of Justice, and the Trusteeship Council.

The UN Charter mandates that the UN and its member states maintain international peace and security, uphold international law, achieve "higher standards of living", address "economic, social, health, and related problems", and promote "universal respect for, and observance of, human rights and fundamental freedoms for all without distinction as to race, sex, language, or religion." As a charter and constituent treaty, it binds all members to its articles, and holds that obligations to the United Nations supersede those of other treaties.

During the Second World War, the Allied powers known as the United Nations officially recognized the need to establish a new postwar international organization. Pursuant to this goal, the UN Charter was discussed, prepared, and drafted during the San Francisco Conference that began 25 April 1945, which involved most of the world's sovereign nations. Following two-thirds approval of each part, the final text was unanimously adopted by the delegates and opened for signature on 26 June 1945; it was signed at the San Francisco War Memorial and Performing Arts Center in San Francisco, United States, by 50 of the 51 original member countries.

The Charter entered into force on 24 October 1945, after being ratified by the original five permanent members of the United Nations Security Council—the China, the France, the Soviet Union, the United Kingdom, and the United States—and a majority of the other signatories. Subsequently, 24 October was later declared as United Nations Day by the United Nations General Assembly. The first UN General Assembly, representing the 51 original members, opened in London on January 10, 1946. On the fourth anniversary of the Charter's entry into force, the cornerstone was laid for the pre