This document discusses the evolution of exchange rate systems over the past 100 years. It describes several major international monetary systems: bimetallism before 1875 when currencies were pegged to gold and silver; the classical gold standard from 1875-1914 when currencies were pegged only to gold; the interwar period from 1915-1944 when currency fluctuations were wide; the Bretton Woods system from 1945-1972 when the US dollar was pegged to gold; and the flexible exchange rate regime since 1973 when currencies floated freely against each other. The document provides details on the key features of each system and how they shaped international exchange rates over time.