When a country becomes a Member of the United Nations, it agrees to accept the obligations of the UN Charter, an international treaty which sets out basic principles of international relations.

The Charter was adopted at a conference in San Francisco in June, 1945 and was officially recognized by the majority of the 51 founding members on October 24, 1945 - what is now known as UN Day. 137 other countries have since signed the Charter and become members of the UN. The UN and its Charter grew out of a plan that began on board a battleship in the Atlantic Ocean in 1941, when President Franklin D. Roosevelt of the USA and Prime Minister Winston Churchill of the United Kingdom met to start discussing how to ensure peace after the end of the Second World War. They later discussed the plan with Joseph Stalin, Leader of the Soviet Union, at a meeting in Yalta, USSR, in 1945.

The Preamble to the Charter sets out the main tenets of the organization:

WE THE PEOPLES OF THE UNITED NATIONS DETERMINED to save succeeding generations from the scourge of war, which twice in our lifetime has brought untold sorrow to humankind, and to reaffirm faith in fundamental human rights, in the dignity and worth of the human person, in the equal rights of men and women and of nations large and small, and to establish conditions under w hich justice and respect for the obligations arising from treaties and other sources of international law can be maintained, and to promote social progress and better standards of life in larger freedom,

AND FOR THESE ENDS to practice tolerance and live together in peace with one another as good neighbours, and to unite our strength to maintain international peace and security, and to ensure, by the acceptance of principles and the institution of methods, that armed force shall not be used, save in the common interest, and to employ international machinery for the promotion of the economic and social advancement of all peopled,

HAVE RESOLVED TO COMBINE OUR EFFORTS TO ACCOMPLISH THESE AIMS. Accordingly , our respective Governments, through representatives assembled in the city of San Francisco, who have exhibited their full powers found to be in good and due form, have agreed to the present Charter of the United Nations and do hereby establish an international organization to be known as the United Nations.