The sheer size of the forex, or foreign exchange, market dominates all others — even the stock market. Every payment that crosses currencies contributes to its fluctuations and momentum. And without a centralized marketplace, forex activity buzzes practically without cease, with traders waking up and doing business everywhere, in every time zone. To get a piece of the action, you need a forex brokerage with best-in-class technology and stellar support.
Factors like interest rates, trade flows, tourism, economic strength and geopolitical risk affect supply and demand for currencies, which creates daily volatility in the forex markets. An opportunity exists to profit from changes that may increase or reduce one currency's value compared to another. A forecast that one currency will weaken is essentially the same as assuming that the other currency in the pair will strengthen because currencies are traded as pairs.

By contrast, the AUD/NZD moves by 50-60 pips a day, and the USDHKD currency pair only moves by an average of 32 pips a day (when looking at the value of currency pairs, most will be listed with five decimal points. A 'Pip' is 0.0001. So, if the EUR/USD moved from 1.16667 to 1.16677, that would represent a 1 pip change). The major Forex pairs tend to be the most liquid, and therefore provide the most opportunities for short-term trading.
Cross Currency Pairs signifies secondary currencies traded against each other and not against the U.S. dollar. Examples include Euro vs. the Japanese Yen (EUR/JPY) or the British Pound vs. Swiss Franc (GBP/CHF). Most reputable brokers offer this category of trades, and it’s especially important for a forex trading account denominated in a currency other than the U.S. dollar, or for more advanced traders capitalizing on discrepancies between other economies.

Due to the ultimate ineffectiveness of the Bretton Woods Accord and the European Joint Float, the forex markets were forced to close[clarification needed] sometime during 1972 and March 1973.[43] The largest purchase of US dollars in the history of 1976[clarification needed] was when the West German government achieved an almost 3 billion dollar acquisition (a figure is given as 2.75 billion in total by The Statesman: Volume 18 1974). This event indicated the impossibility of balancing of exchange rates by the measures of control used at the time, and the monetary system and the foreign exchange markets in West Germany and other countries within Europe closed for two weeks (during February and, or, March 1973. Giersch, Paqué, & Schmieding state closed after purchase of "7.5 million Dmarks" Brawley states "... Exchange markets had to be closed. When they re-opened ... March 1 " that is a large purchase occurred after the close).[44][45][46][47]
The foreign exchange market is unique for several reasons, mainly because of its size. Trading volume in the forex market is generally very large. As an example, trading in foreign exchange markets averaged $5.1 trillion per day in April 2016, according to the Bank for International Settlements, which is owned by 60 central banks and is used to work in monetary and financial responsibility. 
One unique aspect of this international market is that there is no central marketplace for foreign exchange. Rather, currency trading is conducted electronically over-the-counter (OTC), which means that all transactions occur via computer networks between traders around the world, rather than on one centralized exchange. The market is open 24 hours a day, five and a half days a week, and currencies are traded worldwide in the major financial centers of London, New York, Tokyo, Zurich, Frankfurt, Hong Kong, Singapore, Paris and Sydney—across almost every time zone. This means that when the trading day in the U.S. ends, the forex market begins anew in Tokyo and Hong Kong. As such, the forex market can be extremely active any time of the day, with price quotes changing constantly.