Global over-the-counter (OTC) market for the trading of all currencies - the United Nations recognizes 180 different currencies used with over 195 countries. The United States Dollar (USD) is the most popular with over 66 countries using the USD or pegging their currency to it. The decentralized global FX market determines the foreign exchange rate by including all aspects of buying, selling and exchanging currencies at current or future market prices. The FX market has the largest trading market volume in the world.