The Louis d'or is any number of French coins first introduced by Louis XIII in 1640. The name derives from the depiction of the portrait of King Louis on one side of the coin; the French royal coat of arms is on the reverse. The coin was replaced by the French franc at the time of the revolution and later the similarly valued Napoléon. The actual value of the coins fluctuated according to monetary and fiscal policy, but in 1726 the value was stabilized.

A coin is a small object, usually round and flat, used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in large quantities at a mint in order to facilitate trade. They are most often issued by a government. Coins often have images, numerals, or text on them. The faces of coins or medals are sometimes called the obverse and the reverse, referring to the front and back sides, respectively. The obverse of a coin is commonly called heads, because it often depicts the head of a prominent person, and the reverse is known as tails.