The United Nations Charter is the constitution of the United Nations. It was signed at San Francisco on 26th June 1945 by the 50 original member countries. It entered into force on 24th October 1945, after being ratified by the five permanent members of the Security Council (China,France, the Soviet Union, the United Kingdom and the United States), and a majority of the other signatories.
As a treaty, all signatories are bound by international law to obey the provisions of the Charter.
Status of the Charter in the United States
The United Nations Charter has been enacted into law in the United States by virtue of its being ratified as a treaty, making it binding on the executive branch of the government. This is relevant to the Bush doctrine of pre-emptive war which seems on first impression to violate the Charter.