Hedge funds as speculators

About 70% to 90% of the foreign exchange transactions are speculative. In other words, the person or institution that bought or sold the currency has no plan to actually take delivery of the currency in the end; rather, they were solely speculating on the movement of that particular currency. Hedge funds have gained a reputation for aggressive currency speculation since 1996. They control billions of dollars of equity and may borrow billions more, and thus may overwhelm intervention by central banks to support almost any currency, if the economic fundamentals are in the hedge funds' favor

Investment management firms

Investment management firms (who typically manage large accounts on behalf of customers such as pension funds and endowments) use the foreign exchange market to facilitate transactions in foreign securities. For example, an investment manager bearing an international equity portfolio needs to purchase and sell several pairs of foreign currencies to pay for foreign securities purchases.
Some investment management firms also have more speculative specialist currency overlay operations, which manage clients' currency exposures with the aim of generating profits as well as limiting risk. Whilst the number of this type of specialist firms is quite small, many have a large value of assets under management (AUM), and hence can generate large trades.

Retail foreign exchange brokers
Retail traders (individuals) are an explosively growing part of this market, both in size and importance. Currently, they participate indirectly through brokers or banks. Retail brokers, while largely controlled and regulated in the USA by the CFTC and NFA have in the past been subjected to periodic foreign exchange scams. To deal with the issue, the NFA and CFTC began (as of 2009) 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.
There are two main types of retail FX brokers offering the opportunity for speculative currency trading: Retail brokers who employ the "Agency Broker" model and Market-Makers who employ the "Broker as principal or specialist" model. "Agency Brokers" serve as 'your representative' in the broader FX market, by seeking the best prices for your orders, and then typically pass your orders through to some other market-maker, bank or dealer, after applying a small mark-up. Market-Makers, by contrast, typically play the role of 'final resting stop' for your orders by choosing to simply fill them immediately and then manage the resulting risk themselves. No one model is better than the other, and both have various benefits, advantages and drawbacks.
Nonetheless, it is not widely understood that some retail brokers (market makers) typically trade 'against' their clients (via the broker as "principal" model rather than the "agency" broker model) and frequently take the other side of their customers' trades. This may sometimes create a potential conflict of interest and give rise to some of the unpleasant trade-execution experiences some traders & customers 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 cautious optimism is still advised.
The earliest Retail FX brokers were CMC Markets, SAXO Bank (Formerly MIDAS), FXCM (formerly Shalish Capital Markets) GFT (Global Forex Trading) MG Forex (AKA "Money Garden"), eForex.com, and Matchbook FX, which was notable because it was the 1st and only FX broker that pursued a user-price driven ECN model, rather than a Dealer/Market Maker model.
[edit] 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. Send Money Home offer an in-depth comparison into the services offered by all the major non-bank foreign exchange companies.
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.