The Forex or Foreign Exchange market refers to the trading of global currencies. It is the largest financial market in the world, with over $5 trillion traded daily. The United States dollar, euro, Japanese yen and British pound are the most heavily traded currencies. London controls the largest share of Forex trading volume at 31.3%. Factors like interest rates, economic growth, geopolitics, and trade/capital flows influence currency values in this decentralized global market.