The United States dollar is the official currency of the United States of America. It is divided into 100 cents. The U.S. dollar is the currency most used in international transactions and is one of the world's reserve currencies. Several countries use it as their official currency, in many others it is the de facto currency.
The Constitution of the United States of America provides that the United States Congress shall have the power "to coin money". Laws implementing this power are currently codified in Section 5112 of Title 31 of the United States Code. Section 5112 provides in which forms the United States dollars shall be issued. Those coins are both designated in Section 5112 as "legal tender" in payment of debts. The Sacagawea dollar is one example of the copper alloy dollar. The pure silver dollar is known as the American Silver Eagle. Section 5112 also provides for the minting and issuance of other coins, which have values ranging from one-hundredth of one dollar to fifty dollars. These other coins are more fully described in Coins of the United States dollar.
The Constitution provides that "a regular Statement and Account of the Receipts and Expenditures of all public Money shall be published from time to time". That provision of the Constitution is made specific by Section 331 of Title 31 of the United States Code. The sums of money reported in the "Statements" are currently being expressed in U.S. dollars (for example, see the 2009 Financial Report of the United States Government). The U.S. dollar may therefore be described as the unit of account of the United States.
The word "dollar" is one of the words in the first paragraph of Section 9 of Article 1 of the U.S. Constitution. In that context, "dollars" is a reference to the Spanish milled dollar, a coin that had a monetary value of 8 Spanish units of currency, or reales. In 1792 the U.S. Congress adopted legislation to establish a mint, and regulating the Coins of the United States. Section 9 of that act authorised the production of various coins, including "DOLLARS OR UNITS—each to be of the value of a Spanish milled dollar as the same is now current, and to contain three hundred and seventy-one grains and four sixteenth parts of a grain of pure, or four hundred and sixteen grains of standard silver". Section 20 of the act provided, "That the money of account of the United States shall be expressed in dollars, or units... and that all accounts in the public offices and all proceedings in the courts of the United States shall be kept and had in conformity to this regulation". In other words, this act designated the United States dollar as the unit of currency of the United States.
The U.S. dollar bill uses the decimal system, consisting of 100 equal cents (symbol ¢). It is also officially divided into 1,000 mills or ten dimes, while ten dollars is equal to an eagle. However, only cents are in everyday use as divisions of the dollar; "dime" is used solely as the name of the coin with the value of 10¢, while "eagle" and "mill" are largely unknown to the general public, though mills are sometimes used in matters of tax levies, and gasoline prices are usually in the form of $X.XX9 per gallon, e.g., $3.599, sometimes written as $3.599⁄10. When currently issued in circulating form, denominations equal to or less than a dollar are emitted as U.S. coins while denominations equal to or greater than a dollar are emitted as Federal Reserve notes (with the exception of gold, silver and platinum coins valued up to $100 as legal tender, but worth far more as bullion). Both one-dollar coins and notes are produced today, although the note form is significantly more common. In the past, "paper money" was occasionally issued in denominations less than a dollar (fractional currency) and gold coins were issued for circulation up to the value of $20 (known as the "double eagle," discontinued in the 1930s). The term eagle was used in the Coinage Act of 1792 for the denomination of ten dollars, and subsequently was used in naming gold coins. In 1854, James Guthrie, then Secretary of the Treasury, proposed creating $100, $50 and $25 gold coins, which were referred to as a "Union," "Half Union," and "Quarter Union," thus implying a denomination of 1 Union = $100.
Today, USD notes are made from cotton fiber paper, unlike most common paper, which is made of wood fiber. U.S. coins are produced by the United States Mint. U.S. dollar banknotes are printed by the Bureau of Engraving and Printing, and, since 1914, have been issued by the Federal Reserve. The "large-sized notes" issued before 1928 measured 7.42 inches (188 mm) by 3.125 inches (79.4 mm); small-sized notes, introduced that year, measure 6.14 inches (156 mm) by 2.61 inches (66 mm) by 0.0043 inches (0.11 mm).
Always remember that trading foreign exchange on margin carries a HIGH LEVEL OF RISK, and may not be suitable for all investors. Before deciding to trade foreign exchange you should carefully consider your investment objectives, level of experience, and risk appetite. The possibility exists that you could sustain a loss of some or all of your initial investment and therefore you should not invest money that you cannot afford to lose. You should be aware of all the risks associated with foreign exchange trading, and seek advice from an independent financial advisor if you have any doubts.