The main trading centers are London and New York City, though Tokyo, Hong Kong, and Singapore are all important centers as well. Banks throughout the world participate. Currency trading happens continuously throughout the day; as the Asian trading session ends, the European session begins, followed by the North American session and then back to the Asian session.
Unlike a stock market, the foreign exchange market is divided into levels of access. At the top is the interbank foreign exchange market, which is made up of the largest commercial banks and securities dealers. Within the interbank market, spreads, which are the difference between the bid and ask prices, are razor sharp and not known to players outside the inner circle. The difference between the bid and ask prices widens (for example from 0 to 1 pip to 1–2 pips for currencies such as the EUR) as you go down the levels of access. 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 foreign exchange market are determined by the size of the "line" (the amount of money with which they are trading). The top-tier interbank market accounts for 51% of all transactions. From there, smaller banks, followed by large multi-national corporations (which need to hedge risk and pay employees in different countries), large hedge funds, and even some of the retail market makers. According to Galati and Melvin, “Pension funds, insurance companies, mutual funds, and other institutional investors have played an increasingly important role in financial markets in general, and in FX markets in particular, since the early 2000s.” (2004) In addition, he notes, “Hedge funds have grown markedly over the 2001–2004 period in terms of both number and overall size”. Central banks also participate in the foreign exchange market to align currencies to their economic needs.
Meanwhile, daily interbank settlements are also a mover of these markets as forex or broker-dealers, such as banks, are amongst the biggest participants in the forex market. Since these dealers interact with each other, this market is referred to as the interbank market. Large corporations, including exporters and importers, will also use the FX market to hedge currency exposure in order to prevent losses due to the fluctuating value of currencies.
Currencies are always traded in pairs, so the "value" of one of the currencies in that pair is relative to the value of the other. This determines how much of country A's currency country B can buy, and vice versa. Establishing this relationship (price) for the global markets is the main function of the foreign exchange market. This also greatly enhances liquidity in all other financial markets, which is key to overall stability.
There are a number of main-players in the Forex market, including central banks, commercial banks, and investment banks. This is known as the interbank market, as they constantly deal with each other on behalf of themselves or their customers. There are a number of other participants in the foreign exchange market, however, which also includes large multinational corporations, global money managers, registered dealers, international money brokers, futures and options traders and individual investors.
The foreign exchange market – also called forex, FX, or currency market – was one of the original financial markets formed to bring structure to the burgeoning global economy. In terms of trading volume it is, by far, the largest financial market in the world. Aside from providing a venue for the buying, selling, exchanging and speculation of currencies, the forex market also enables currency conversion for international trade settlements and investments. According to the Bank for International Settlements (BIS), which is owned by central banks, trading in foreign exchange markets averaged $5.1 trillion per day in April 2016.
The need to exchange currencies is the primary reason why the forex market is the largest, most liquid financial market in the world. It dwarfs other markets in size, even the stock market, with an average traded value of around U.S. $2,000 billion per day. (The total volume changes all the time, but as of August 2012, the Bank for International Settlements (BIS) reported that the forex market traded in excess of U.S. $4.9 trillion per day.)