The foreign exchange (currency or forex or FX) market exists wherever one currency is traded for another. It is by far the largest financial market in the world, and includes trading between large banks, central banks, currency speculators, multinational corporations, governments, and other financial markets and institutions. The average daily trade in the global forex and related markets currently is over US$ 3 trillion.

Because foreign exchange is an OTC market where brokers/dealers negotiate directly with one another, there is no central exchange or clearing house. The biggest geographic trading centre is the UK, primarily London.

Unlike a stock market, where all participants have access to the same prices, the forex market is divided into levels of access. At the top is the inter-bank market, which is made up of the largest investment banking firms. Within the inter-bank market, spreads, which are the difference between the bid and ask prices, are razor sharp and usually unavailable, and not known to players outside the inner circle. As you descend the levels of access, the difference between the bid and ask prices widens (from 0-1 pip to 1-2 pips only for major currencies like the Euro). This is due to volume. If a trader can guarantee large numbers of transactions for large amounts, they can demand a smaller difference between the bid and ask price, which is referred to as a better spread. The levels of access that make up the forex market are determined by the size of the “line” (the amount of money with which they are trading). The top-tier inter-bank market accounts for 53% of all transactions.

Electronic trading is growing in the FX market, and algorithmic trading is becoming much more common. There is much confusion about the technique. According to financial consultancy Celent estimates, by 2008 up to 25% of all trades by volume will be executed using algorithm, up from about 18% in 2005.

A forex scam is any trading scheme used to defraud individual traders by convincing them that they can expect to gain an unreasonably high profit by trading in the foreign exchange market, which would be a zero-sum game were it not for the fact that there are brokerage commissions, which technically make forex a "negative-sum" game.