Constitutes

Currencies are traded against one another. Each pair of currencies thus constitutes an individual product and is traditionally noted XXX/YYY, where YYY is the ISO 4217 international three-letter code of the currency into which the price of one unit of XXX is expressed (called base currency). For instance, EUR/USD is the price of the euro expressed in US dollars, as in 1 euro = 1.5465 dollar. Out of convention, the first currency in the pair, the base currency, was the stronger currency at the creation of the pair. The second currency, counter currency, was the weaker currency at the creation of the pair

Purchasing powet parity
Fluctuations in exchange rates are usually caused by actual monetary flows as well as by expectations of changes in monetary flows caused by changes in gross domestic product (GDP) growth, inflation (purchasing power parity theory), interest rates (interest rate parity, Domestic Fisher effect, International Fisher effect), budget and trade deficits or surpluses, large cross-border M&A deals and other macroeconomic conditions. Major news is released publicly, often on scheduled dates, so many people have access to the same news at the same time. However, the large banks have an important advantage; they can see their customers'

Trading center
The main trading center is London, but New York, 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, excluding weekends

Majority
There is no unified or centrally cleared market for the majority of FX trades, and there is very little cross-border regulation. Due to the over-the-counter (OTC) nature of currency markets, there are rather a number of interconnected marketplaces, where different currencies instruments are traded. This implies that there is not a single exchange rate but rather a number of different rates (prices), depending on what bank or market maker is trading, and where it is. In practice the rates are often very close, otherwise they could be exploited by arbitrageurs instantaneously. Due to London's dominance in the market, a particular currency's quoted price is usually the London market price. A joint venture of the Chicago Mercantile Exchange and Reuters, called Fxmarketspace opened in 2007 and aspired but failed to the role of a central market clearing mechanism.

Mony transfer companies
Money transfer companies/remittance companies perform high-volume low-value transfers generally by economic migrants back to their home country. In 2007, the Aite Group estimated that there were $369 billion of remittances (an increase of 8% on the previous year). The four largest markets (India, China, Mexico and the Philippines) receive $95 billion. The largest and best known provider is Western Union with 345,000 agents globally.

Non-bank foreign exchange companies
Non-bank foreign exchange companies offer currency exchange and international payments to private individuals and companies. These are also known as foreign exchange brokers but are distinct in that they do not offer speculative trading but currency exchange with payments. I.e., there is usually a physical delivery of currency to a bank account.
It is estimated that in the UK, 14% of currency transfers/payments[10] are made via Foreign Exchange Companies.[11] These companies' selling point is usually that they will offer better exchange rates or cheaper payments than the customer's bank. These companies differ from Money Transfer/Remittance Companies in that they generally offer higher-value services
opportunity
There are two types of retail brokers offering the opportunity for speculative trading: retail foreign exchange brokers and market makers. Retail traders (individuals) are a small fraction of this market and may only participate indirectly through brokers or banks. Retail brokers, while largely controlled and regulated by the CFTC and NFA might be subject to foreign exchange scams.[8][9] At present, the NFA and CFTC are imposing stricter requirements, particularly in relation to the amount of Net Capitalization required of its members. As a result many of the smaller, and perhaps questionable brokers are now gone. It is not widely understood that retail brokers and market makers typically trade against their clients and frequently take the other side of their trades. This can often create a potential conflict of interest and give rise to some of the unpleasant experiences some traders have had. A move toward NDD (No Dealing Desk) and STP (Straight Through Processing) has helped to resolve some of these concerns and restore trader confidence, but caution is still advised in ensuring that all is as it is presented