Federal Reserve Notes in the context of "US$"

The United States dollar (symbol: $; currency code: USD) is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it into 100 cents, and authorized the minting of coins denominated in dollars and cents. U.S. banknotes are issued in the form of Federal Reserve Notes, popularly called greenbacks due to their predominantly green color.

The U.S. dollar was originally defined under a bimetallic standard of 371.25 grains (24.057 g) (0.7734375 troy ounces) fine silver or, from 1834, 23.22 grains (1.505 g) fine gold, or $20.67 per troy ounce. The Gold Standard Act of 1900 linked the dollar solely to gold. From 1934, its equivalence to gold was revised to $35 per troy ounce. In 1971 all links to gold were repealed. The U.S. dollar became an important international reserve currency after the First World War, and displaced the pound sterling as the world's primary reserve currency by the Bretton Woods Agreement towards the end of the Second World War. The dollar is the most widely used currency in international transactions, and a free-floating currency. It is also the official currency in several countries and the de facto currency in many others, with Federal Reserve Notes (and, in a few cases, U.S. coins) used in circulation.

Silver certificates are a type of representative money issued between 1878 and 1964 in the United States as part of its circulation of paper currency. They were produced in response to silver agitation by citizens who were angered by the Fourth Coinage Act, which had effectively placed the United States on a gold standard. The certificates were initially redeemable for their face value of silver dollar coins and later (for one year from June 24, 1967, to June 24, 1968) in raw silver bullion. Since 1968 they have been redeemable only in Federal Reserve Notes and are thus obsolete, but still valid legal tender at their face value and thus are still an accepted form of currency.

Large-size silver certificates, generally 1.5 in (38 mm) longer and 0.5 in (13 mm) wider than modern U.S. paper currency, (1878 to 1923) were issued initially in denominations from $10 to $1,000 (in 1878 and 1880) and in 1886 the $1, $2, and $5 were authorized. In 1928, all United States bank notes were re-designed and the size reduced. The small-size silver certificate (1928–1964) was only regularly issued in denominations of $1, $5, and $10. The complete type set below is part of the National Numismatic Collection at the Smithsonian's National Museum of American History.