A double eagle is a gold coin of the United States with a denomination of $20. (Its gold content of 0.9675 troy ounces [30.09 g] was worth $20 at the 1849 official price of $20.67/ozt.) The coins are 34 mm × 2 mm and are made from a 90% gold (0.900 fine or 21.6 kt) and 10% copper alloy and have a total weight of 1.0750 troy ounces (1.1794 oz; 33.44 g).

The eagle, half eagle, and quarter eagle were defined by name in the act of Congress originally authorizing them. Likewise, the double eagle was created by the Coinage Act of 1849. Since the $20 gold piece had twice the value of the eagle, these coins were designated "double eagles". Before, the most valuable American coin was the $10 gold eagle, first produced in 1795, two years after the United States Mint opened.

The production of the first double eagle coincided with the 1849 California Gold Rush. In that year, the mint produced two pieces in proof. In 1904, President Theodore Roosevelt sought to beautify American coinage, and proposed Augustus Saint-Gaudens as an artist capable of the task. Although the sculptor had poor experiences with the Mint and its chief engraver, Charles E. Barber, Saint-Gaudens accepted Roosevelt's call. The work was subject to considerable delays, due to Saint-Gaudens's declining health and difficulties because of the high relief of his design. Saint-Gaudens died in 1907, after designing the eagle and double eagle, but before the designs were finalized for production. The new coin became known as the Saint-Gaudens double eagle. Regular production continued until 1933, when the official price of gold was changed to $35/ozt by the Gold Reserve Act.

Regular issue double eagles come in two major types and six minor varieties as follows:

Due to the less desirable artwork and therefore lower demand, Liberty Head (Coronet) $20 gold pieces are less often encountered, and the common subtype commands less than the Saint-Gaudens type. In 1866, the motto "In God We Trust" was added to the double eagle, creating a second subtype. In 1877, the coin's denomination design on the reverse was changed from "TWENTY D." to "TWENTY DOLLARS" creating a third and final subtype for the series. An 1879 pattern coin was made for the quintuple Stella using a design combining features of the Liberty Head double eagle and Stella pattern coin and using the same alloy as the Stella (90 parts gold, three parts silver, and seven parts copper); this coin was stolen in July 2008.

The Saint-Gaudens double eagle is named for the designer, Augustus Saint-Gaudens, one of the premier sculptors in American history. Theodore Roosevelt imposed upon him in his last few years to redesign the nation's coinage at the beginning of the 20th century. Saint-Gaudens' work on the high-relief $20 gold piece is considered to be one of the most extraordinary pieces of art on any American coin. The mint eventually insisted on a low-relief version, as the high-relief coin took up to eleven strikes to bring up the details which was harder for the older die presses. This high-relief also caused irregular stacking for banking purposes. Only 12,367 of these coins were struck in 1907. These coins easily top the $10,000 price in circulated grades, but can reach nearly a half million dollars in the best states of preservation.

There were several changes in the early years of this design. The first coins issued in 1907 design featured a date in Roman numerals, but this was changed later that year to the more convenient Arabic numerals. The motto "In God We Trust" was omitted from the initial design, as Roosevelt felt that putting the name of God on money that could be used for immoral purposes was inappropriate. By act of Congress, the motto was added in mid-1908.

The design of the Saint-Gaudens coin was slightly changed once more when New Mexico and Arizona became states in 1912, and the number of stars along the rim was accordingly increased from 46 to 48.