The international monetary system has evolved over time from the Gold Standard to the Bretton Woods system to the current floating exchange rate regime. Under the Gold Standard, currencies were backed by gold reserves and countries maintained fixed exchange rates. The Bretton Woods system established the IMF, pegged currencies to the US dollar which was pegged to gold, and allowed adjustable pegged rates. However, the system collapsed in the 1970s due to US balance of payments deficits. Currently most currencies float freely though some are managed to stabilize rates.