The US dollar, the unit currency of the United States of America (USD). The Congress of the United States on 6 July 1785 the dollar the official currency, US approved. The sixth of July this year 1785 us (at that time, only a parliament), was unanimously of the dollar""the Dollar unit of the money of that country. Before U.S. independence, namely on July 4, 1776, money, United Kingdom (lira) in 13 immigrant ghetto, British North America was common. In the flow of revolution, Americans silver coin of Spain, called "dollar", which in Mexico was common means of trading in put and said, " that's why the name of your national currency "the dollar", though. Coins, silver dollar from the fourteenth century, over three centuries called the "Thaler, etc. injured. and the dollar" in Europe, it was common that Spanish, it is maintained, and to the colonies in the American continent moved made.With a vertical line"$" that marks the international dollar is also from the Spanish borrowed that money with your mark, P (Pi) determined; and this "P" in North America, gradually and in the flow of writing in The Shape of "$" income.