On what date was the United Nations officially founded?

The United Nations was officially founded on 24 October 1945.

The organization came into existence when the United Nations Charter entered into force after being ratified by the required states, including its five future permanent Security Council members. The charter had been signed in San Francisco on 26 June 1945, but signing and founding were separate milestones.

The UN was created in the aftermath of the Second World War to help maintain international peace and security, develop friendly relations among nations, and encourage cooperation on global problems. Its predecessor, the League of Nations, had been established after the First World War but ceased to function effectively during the Second World War.

United Nations Day is observed annually on 24 October. The organization began with 51 member states; membership later expanded to 193, following the admission of South Sudan in 2011.