The United States dollar (sign: $; code: USD) is the unit of currency of the United States and is defined by the Coinage Act of 1792 to be between 371 and 416 grains (27.0 g) of silver (depending on purity). The U.S. dollar is normally abbreviated as the dollar sign, $, or as USD or US$ to distinguish it from other dollar-denominated currencies and from others that use the $ symbol. It is divided into 100 cents.

Taken over by the Congress of the Confederation of the United States on July 6, 1785, the U.S. dollar is the currency most used in international transactions. Although U.S. dollar is a fiat currency, several countries use it as their official currency, and in many others it is the de facto currency.

The U.S. dollar uses the decimal system, consisting of 100 equal cents (symbol ¢). In another division, there are 1,000 mills or ten dimes to a dollar, or 4 quarters to a dollar; additionally, 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 the second half of the 19th century there were occasional discussions of creating a $50 gold coin, which was referred to as a "Half Union," thus implying a denomination of 1 Union = $100. 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. 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).

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).

Grand, sometimes shortened to simply G, is a common term for the amount of $1,000. The suffix k (from "kilo-") is also commonly used to denote this amount (such as "$10k" to mean $10,000). Banknotes' nicknames are usually the same as their values (such as five, twenty, etc.) The $5 bill has been referred to as a "fin" or a "fiver" or a "five-spot;" the $10 bill as a "sawbuck," a "ten-spot," or a "Hamilton"; the $20 bill as a "double sawbuck," a "twomp," a "twenty-banger," or a "Jackson"; the $1 bill is sometimes called a "single," the $2 bill a "deuce" or a "Tom," and the $100 bill is nicknamed the hunsky, a "Benjamin," "Benjie," or "Frank" (after Benjamin Franklin, who is pictured on the note), C-note (C being the Roman numeral for 100), Century Note, or "bill" ("two bills" being $200, etc.). The dollar has also been referred to as a "bone" or "bones" (i.e. twenty bones is equal to $20) or a "bean" for slang on the East Coast (primarily in New York). Occasionally these will be referred to as "dead presidents," although neither Hamilton ($10) nor Franklin ($100) was President. $1000 notes are occasionally referred to as 'large' in banking ("twenty large" being $20,000, etc.). The newer designs are sometimes referred to as "Bigface" bills.

Official United States coins have been produced every day from 1792 to the present. In normal circulation today, there are coins of the denominations 1¢ ([one] cent, also referred to as a penny), 5¢ (nickel), 10¢ (dime), 25¢ (quarter dollar officially, or simply quarter in common usage), 50¢ (half dollar officially, sometimes referred to as a fifty-cent piece), and $1 (dollar officially, but frequently referred to as a dollar coin).

Currently printed denominations are $1, $2, $5, $10, $20, $50, and $100. Notes above the $100 denomination ceased being printed in 1946 and were officially withdrawn from circulation in 1969. These notes were used primarily in inter-bank transactions or by organized crime; it was the latter usage that prompted President Richard Nixon to issue an executive order in 1969 halting their use. With the advent of electronic banking, they became less necessary. Notes in denominations of $500, $1,000, $5,000, $10,000, and $100,000 were all produced at one time.

The dollar is an important international reserve currency along with the euro. The euro inherited this status from the German mark, and since its introduction, has increased its standing considerably, mostly at the expense of the dollar. Despite the dollar's recent losses to the euro, it is still by far the major international reserve currency, with an accumulation more than double that of the euro.

In August 2007, two scholars affiliated with the government of the People's Republic of China threatened to sell its substantial reserves in American dollars in response to American legislative discussion of trade sanctions designed to revalue the Chinese yuan. The Chinese government denied that selling dollar-denominated assets would be an official policy in the foreseeable future.

Former Federal Reserve Chairman Alan Greenspan said in September 2007 that the euro could replace the U.S. dollar as the world's primary reserve currency. It is "absolutely conceivable that the euro will replace the dollar as reserve currency, or will be traded as an equally important reserve currency."

The leu ([lew], plural: lei [lej]; ISO 4217 code RON; numeric code 946) is the currency of Romania. It is subdivided into 100 bani (singular: ban). On 1 July 2005, Romania underwent a currency reform, switching from the previous leu (ROL) to a new leu (RON). 1 RON is equal to 10,000 ROL.

Romania joined the European Union on 1 January 2007 and it is expected to adopt the euro in 2014.

On August 15, 1947, a revaluation took place, with a new leu replacing the old one at a rate of 20,000 old lei = 1 new leu. This revaluation, called a monetary reform or stabilisation measure (mica stabilizare, marea stabilizare), was carried out by the Communist authorities with absolutely no advance warning and without the possibility to exchange more than a fixed amount of money for the new currency. This was done in order to depose the former middle and upper classes of their last assets, after nationalization, to prepare for collectivization and to finalize the installation of communism. At the time of its introduction, 150 new lei equalled 1 U.S. dollar.

In the 1990s, after the downfall of communism, inflation ran high due to reform failures, the legalization of owning foreign currency in 1990, and the bankrupt policies of the former communist era, reaching rates as high as 300% per year in 1993. By September 2003, one euro was exchanged for more than 40,000 lei, this being its peak value. Following a number of successful monetary policies in the late 1990s and early 2000s, the situation became gradually more stable, with one digit inflation in 2005.

The Romanian leu briefly held the dubious distinction of being the world's least valued currency unit, from January (when the Turkish lira dropped six zeros) to July 2005. However, the 1,000,000 lei bill was not the highest Romanian denomination ever. This distinction belongs to the 5 million lei bill from 1947.

On 1 July 2005, the leu was revalued at the rate of 10,000 "old" lei (ROL) for one "new" leu (RON), thus psychologically bringing the purchasing power of the leu back in line with those of other major Western currencies. The term chosen for the action was "denominare", similar to the English "denomination", to signify not a conversion, but rather a total reinvention.

The first day brought difficulties adjusting to the new paper currencies and closed ATMs (that needed reprogramming) and forcing a new calculation habit that slowed down shops and annoyed some salespeople and shoppers. The old ROL currency banknotes remained in circulation until December 31, 2006 (coins remained in circulation only until December 31, 2005), but all accounts have been converted starting July 1, 2005. There is no conversion time limit between the currencies. Retailers had to display prices in both old and new currency from March 1, 2005 until June 30, 2006. The appreciation of the leu during 2005 was about 20% against a basket of major currencies.

As of 2006, the revaluation is a potential source of confusion, especially to visitors, since both old and new currency values are commonly quoted. When written, the very large amounts in old currency are usually obvious, but in speaking inhabitants might refer to an amount of 5 new lei as simply "fifty" in reference to its value 50,000 old lei.

In 1952, coins were introduced in denominations of 1, 3, 5, 10 and 25 bani, with the 1, 3 and 5 struck in aluminium bronze and the others in cupro-nickel. In 1955, cupro-nickel 50 bani were added.

In 1960, a new coinage was introduced, consisting of 15 and 25 bani, with 5 bani, 1 and 3 lei coins added in 1963. All were struck in nickel-clad steel. In 1975, aluminium replaced steel in the 5 and 15 bani, with the same change happening for the 25 bani in 1982. Aluminium 5 lei were introduced in 1978.

Following the end of the communist regime, a new coinage was introduced between 1990 and 1992, consisting of 1 leu in bronze clad steel, 5 and 10 lei in nickel plated steel, 20 and 50 lei in brass clad steel and nickel plated steel 100 lei.

As inflation took its toll, 500, 1000 and 5000 lei coins were introduced in 1999, 2000 and 2001, respectively, and were the only coins circulating when the revaluation occurred. They were all criticized for being clumsy and difficult to use. The 500 lei coins were very thick (about 0.3 cm). Despite their small value, it took only a handful of such coins to fill one's pocket. They were also made of poor material and could be occasionally found with bite marks. The 1000 lei coin was considered too small and was also cheaply made, and the 5000 lei coin was not circular (it was a dodecagon). This made it awkward to handle and difficult to use in slot machines, where it was frequently the only coin accepted. The 500, 1000 and 5000 lei coins became worth 5, 10 and 50 bani with the revaluation.

In 1952, the Ministry of Finance introduced notes for 1, 3 and 5 lei, and the Banca Republicii Populare Romane introduced 10, 25 and 100 lei notes. In 1966, the Banca Nationala a Republicii Socialiste Romania took over the production of all paper money, issuing notes for 1, 3, 5, 10, 25, 50 and 100 lei.

In 1991, 500 and 1000 lei notes were introduced, followed by 200 and 5000 lei notes in 1992, 10,000 lei in 1994, 50,000 lei in 1996, 100,000 lei in 1998, 500,000 lei in 2000 and 1 million lei in 2003. There was also a 2000 lei note, introduced in 1999; it celebrated the total solar eclipse that occurred on August 11th, 1999. The final issues of the 2000, 10,000, 50,000, 100,000, 500,000 and 1 million lei were polymer notes.

Notes in circulation at the revaluation were:

* 10,000 lei (became 1 leu)
* 50,000 lei (became 5 lei)
* 100,000 lei (became 10 lei)
* 500,000 lei (became 50 lei)
* 1,000,000 lei (became 100 lei)

In 2005, polymer notes were introduced for 1, 5, 10, 50, 100 and 500 lei. 200 lei notes were added in 2006. The designs of the 1, 5, 10, 50 and 100 lei notes are based on those of the earlier 10,000, 50,000, 100,000, 500,000 and 1 million lei notes which they replaced. The 10 lei bill was redesigned in November 2008 (most of the graphic elements are identical, some of the safety elements were withdrawn, making its safety degree similar the the lower values of 1 leu and 5 lei bills).