The dollar (currency code USD) is the unit of currency of the United States. The U.S. dollar has also been adopted as the official and legal currency by the governments in a few other countries. 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.

Adopted 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. Several countries use the U.S. dollar as their official currency, and many others allow it to be used in a de facto capacity. In 1995, over US $380 billion were in circulation, two-thirds of which was outside the United States. By 2005, that figure had doubled to nearly $760 billion, with an estimated half to two-thirds being held overseas, representing an annual growth rate of about 7.6%. However, as of December 2006, the dollar was surpassed by the euro in terms of combined value of cash in circulation. Since then the current value of euro cash in circulation has risen to more than €695 billion, equivalent to US$1,029 billion at current exchange rates.