Usd is a currency called UnitedStatesdollar, which is also called US dollar. The dollar is the official currency of the United States. At present, the US dollar banknotes in circulation are all the banknotes issued since 1929. At present, the issuance of US dollars is controlled by the Federal Reserve system. The most commonly used symbol of the dollar is "$".

The competent department for issuing US dollars is Congress, and the Federal Reserve Bank is responsible for the specific issuance business. After World War II, continental European countries reached an agreement with the United States to use US dollars for international payments. Since then, the dollar has been widely used as a reserve currency in countries outside the United States, and eventually became an international currency.

The main scene pattern on the front of the US dollar bill is a person's head, and the main color is black. The main landscape pattern on the back is architecture, and the main color is green, but there is little difference between different versions, such as the back of 1934 is dark green, the back of 1950 is grass green, and the back of 1963 is dark green. Because dollar green is an ink made of tree juice, the quality of tree juice is different every time, so the color is slightly different.

The signature on the dollar bill is the signature of the finance minister, and different finance ministers issue it in different years. Before the 20th century, 1, 5, 10, 25,50-cent banknotes were issued. Compared with the small front page dollar, the big front page dollar is half the size of the small front page dollar. Interestingly, all denominations of dollars are the same size, and $20 is the most used high-denomination banknote in the United States.