The United States dollar (sign: $; code: USD; also abbreviated US$ and referred to as the dollar, U.S. dollar, or American dollar) is the official currency of the United States and its insular territories per the United States Constitution since 1792. For most practical purposes, it is divided into 100 smaller cent (¢) units, but is occasionally divided into 1000 mills (₥) for accounting purposes. The circulating paper money consists of Federal Reserve Notes that are denominated in United States dollars (12 U.S.C. § 418).
Since the suspension in 1971 of convertibility of paper U.S. currency into any precious metal, the U.S. dollar is, de facto, fiat money. As it is the most used in international transactions, the U.S. dollar is the world’s primary reserve currency. Several countries use it as their official currency, and in many others it is the de facto currency. Besides the United States, it is also used as the sole currency in two British Overseas Territories in the Caribbean: the British Virgin Islandsand Turks and Caicos Islands. A few countries use the Federal Reserve Notes for paper money, while still minting their own coins, or also accept U.S. dollar coins (such as the Sacagawea or presidential dollar). As of September 20, 2017, there were approximately $1.58 trillion in circulation, of which $1.53 trillion was in Federal Reserve notes (the remaining $50 billion is in the form of coins).
Article I, Section 8 of the U.S. Constitution provides that the Congress has the power “To coin money”. Laws implementing this power are currently codified at 31 U.S.C. § 5112. Section 5112 prescribes the forms in which the United States dollars should be issued. These 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 cent to 100 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 I of the Constitution. There, “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 passed a Coinage Act. Section 9 of that act authorized 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.
Unlike the Spanish milled dollar, the U.S. dollar is based upon a decimal system of values. In addition to the dollar the coinage act officially established monetary units of mill or one-thousandth of a dollar (symbol ₥), cent or one-hundredth of a dollar (symbol ¢), dime or one-tenth of a dollar, and eagle or ten dollars, with prescribed weights and composition of gold, silver, or copper for each. It was proposed in the mid-1800s that one hundred dollars be known as a union, but no union coins were ever struck and only patterns for the $50 half union exist. 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, more commonly 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. Paper currency less than one dollar in denomination, known as “fractional currency”, was also sometimes pejoratively referred to as “shinplasters”. 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 by 3.125 inches (188.5 by 79.4 mm); small-sized notes, introduced that year, measure 6.14 by 2.61 by 0.0043 inches (155.96 by 66.29 by 0.11 mm). When the current, smaller sized U.S. currency was introduced it was referred to as Philippine-sized currency because the Philippines had previously adopted the same size for its legal currency.