Money is the official medium of exchange issued by a government. It is comprised of bills and coins. The type of money used is specific to an individual country, though some countries share the same currency; for example, a number of countries use the Euro or the U.S. Dollar as their official currency. The value of money is based on the denomination stated on the face of a bill or coin. Depending on the rate of inflation, the amount of value that can be obtained in exchange for a stated denomination will change. A currency exchange rate is used to buy the currency of a different country; this rate varies based on the relative demand for each currency, the relative interest rates in the two countries, and other factors.