The spot foreign exchange market (forex, FX, or currency market), is where the buying and selling of different world currencies takes place. The price of one currency in terms of another is called an exchange rate, and it is this forex market that determines the relative values of currencies at any given time.

The market itself is actually a worldwide network of a variety of buyers and sellers, connected by telephone lines and computer screens—there is no central headquarters or exchange. Three main global financial centers handle the majority of all FX transactions—United Kingdom, United States, and Japan. Currency transactions in Singapore, Switzerland, Hong Kong, Germany, France and Australia account for most of the remaining transactions in the market.

Trading takes place round the clock, with exception to weekends, from 22:00 GMT on Sunday, until 22:00 GMT on Friday. For example, the London market is opening at 8 a.m. (08:00 GMT), while the trading day is ending in Singapore and Hong Kong. The New York market opens for business at 9:30 a.m. local time while London traders are just returning from lunch at 2:30 p.m. (14:30 GMT). Later, San Francisco begins to conduct business as London and Europe close for the day. And as the market closes in San Francisco, the Singapore and Hong Kong markets are starting a fresh day at 8 a.m. local time (00:00 GMT).

The FX market is fast-paced, volatile and enormous—it is the largest and most liquid market in the world. In 2008, on average, an estimated $3.2 trillion exchanged hands each day.