The way currencies fluctuate in value is determined by a number of factors. One of them is the type of currency and how it reacts to changes in the prices of other currencies. The first distinction to be made is between fiat and commodity currencies. Historically, money was usually printed on a commodity (gold and silver coins, for example.) This form of money is practical in that the physical monetary item has some intrinsic worth. It also means that the supply of money in a given economy cannot be easily manipulated.