The modern foreign exchange (FX or Forex) market started forming during the 1970s when countries gradually switched to floating exchange rates from the previous exchange rate regime, which remained fixed as per the Bretton Woods system.
Foreign Exchange is one of the largest and most liquid financial markets in the world is the largest financial market in the world, with a volume of over $4 trillion a day and evidence suggests that the market is still expanding. If you compare that to the $25 billion a day volume that the New York Stock Exchange trades, you can easily see how enormous the Foreign Exchange really is. It actually equates to more than three times the total amount of the stocks and futures markets combined! More.