Before 1933, the eagle was the largest of the five main decimal base-units of a denomination in the United States. These five main base-units of the denomination were the mill, the cent, the dime, the dollar, and the eagle. A cent was equal to 10 mills, a dime is equal to 10 cents, a dollar is equal to 10 dimes, and an eagle is equal to 10 dollars.

The eagle was the base-unit of the denomination in gold such as a double eagle showed its value as twenty dollars.

There is a difference between United States' circulating eagle denomination from the late 18th century and 20th century the American Eagle bullion coins which are manufactured from silver or gold (since 1986), platinum (since 1997), or palladium.

Gold eagles were issued for circulation in three phases i.e., from 1795–1933, half eagles from 1795–1929, quarter eagles from 1796–1929, and double eagles from 1850–1933. Except for double eagle, the diameters of all other denominations were decreased over time.