Monaco has been closely linked to France since 1918, when a treaty made between the two countries formalized France's commitment to defend Monaco and respect its sovereignty "so long as it is exercised in conformity with the political, military, naval, and economic interests of France." During his reign, Prince Rainier has negotiated two additional treaties of significance (in 1954 and 1963) with France, updating but not fundamentally altering this relationship. France may station troops in Monaco and make use of Monaco's territorial waters because of the customs union arranged with France.
Monaco is closely associated with the economic apparatus of the European Union (EU) through its customs union with France and its reliance on the euro (previously the French franc) as official currency.
Monaco sends ambassadors to the Vatican, Paris, and a few European capitals. France finally allowed Monaco to join the United Nations (UN) in 1993. The principality is a member of the UN Educational, Scientific, and Cultural Organization (UNESCO) and other affiliated UN organizations. It also participates in the Conference for European Security and Cooperation. Several international organizations have their headquarters in Monaco, including the International Commission for the Scientific Exploration of the Mediterranean Sea, the International Hydrographic Bureau, and the International Commission for Legal-Medical Problems. It is also the seat for the International Academy of Tourism, founded in 1951 by Prince Rainier III.