The foreign exchange market (Forex, FX, or currency market) is a global decentralized or over-the-counter (OTC) market for the trading of currencies. ... The main participants in this market are the larger international banks.

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These rates are usually pegged to the U.S. dollar. Their central banks have enough money in their foreign currency reserves to control how much their currency is worth. To keep the exchange rate fixed, the central bank holds U.S. dollars. It also increases the supply of dollars, sending its value down.