What is currency? In recent years this term has been popularized and is no longer part of the language used by financial experts. To make it clear what currency is, we can define it as the monetary unit of a country. After the economic crisis of 1929 all capitalists currencies became currency paper, this caused that all currencies were volatile and were tied to the crises, to problems such as inflation that takes away purchasing power to the currency. The currencies of the capitalist countries are divided into convertible to other currencies, limited convertibility and closed, or currencies that can be used within the borders of a country. The currency convertibility is something relatively new seeing that until 1958, convertible currencies were only the American dollar, the Swiss franc and the Portuguese escudo. Since then most of the currencies became convertible. In the capitalist world, the currency used for most of the international transactions, is the dollar, nevertheless, the fall in world domination by the power of the north has caused that the dollar currency suffers a fall especially in the last years. The diversification of currency for the payment of international transactions is a clear example of the economy globalization and the collapse of the United States, since in recent years the German mark, the French franc and the Italian lyre have been popularized for international payments. The equation is simple, as the strength of the United States in the economy in the capitalist world comes down, the positions of the fundamental capitalist currency will significantly weaken ; North American dollar and other currencies gain ground.