International monetary systems provide means of payment between buyers and sellers of different nationalities and facilitate international trade and investment. They have evolved over five stages: 1) Bimetallism before 1875 used both gold and silver coins but was unstable, 2) the Classical gold standard from 1875-1914 tied currencies to gold, 3) the Interwar period from 1915-1944 saw suspension of the gold standard and competitive currency depreciation, 4) the Bretton Woods system from 1945-1972 established the IMF and pegged currencies to the US dollar and gold, and 5) the Flexible exchange rate system since 1973 allows currencies to float against each other after the collapse of Bretton Woods.