The Floating Exchange Rate
There are two main systems used to determine a currency's exchange rate: floating currency and pegged currency.
The market determines a floating exchange rate. In other words, a currency is worth whatever buyers are willing to pay for it. This is determined by supply and demand, which is in turn driven by foreign investment, import/export ratios, inflation, and a host of other economic factors.
Generally, countries with mature, stable economic markets will use a floating system. Virtually every major nation uses this system, including the U.S., Canada and Great Britain. Floating exchange rates are considered more efficient, because the market will automatically correct the rate to reflect inflation and other economic forces.
The floating system isn't perfect, though. If a country's economy suffers from instability, a floating system will discourage investment. Investors could fall victim to wild swings in the exchange rates, as well as disastrous inflation.