The primary factors that influence exchange rates are the balance of international payments for goods and services, the state of the economy, political developments as well as various other psychological factors. In addition, fundamental economic forces such as inflation and interest rates will constantly influence currency prices. In addition Central banks sometimes participate in the FOREX market by buying extremely large sums of one currency for another - this is referred to as Central Bank intervention. Central banks can also influence currency prices by changing their country's short-term interest rate to make it relatively more or less attractive to foreigners. Any of these broad-based economic conditions can cause sudden and dramatic currency price swings. The fastest moves, however, occur usually when information is released that is unexpected by the market at large. This is a key concept because what drives the currency market in many cases is the anticipation of an economic condition rather than the condition itself.
Activities by professional currency managers, generally on behalf of a pool of funds, have also become a factor moving the market. While professional managers may behave independently and view the market from a unique perspective, most, if not all, are at least aware of important technical chart points in each major currency. As the market approaches major 'support' or 'resistance' levels, price-action becomes more technically oriented and the reactions of many managers are often predictable and similar. These market periods may also result in sudden and dramatic price swings. Traders make decisions on both technical factors and economic fundamentals. Technical traders use charts to identify trading opportunities whereas fundamentalists predict movements in exchange rates by interpreting a wide variety of data, which range from breaking news to economic reports. 

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