The Monroe Doctrine Centennial half dollar was a fifty-cent piece struck by the United States Bureau of the Mint. Bearing portraits of former U.S. Presidents James Monroe and John Quincy Adams, the coin was issued in commemoration of the centennial of the Monroe Doctrine and was produced at the San Francisco Mint in 1923. Sculptor Chester Beach is credited with the design, although the reverse closely resembles an earlier work by Raphael Beck.

The half dollar, sometimes referred to as the half for short or 50-cent piece, is a United States coin worth 50 cents, or one half of a dollar. In both size and weight, it is the largest United States circulating coin currently produced, being 1.205 inches in diameter and 0.085 in (2.16 mm) in thickness, and is twice the weight of the quarter. The coin's design has undergone a number of changes throughout its history. Since 1964, the half dollar depicts the profile of President John F. Kennedy on the obverse and the seal of the president of the United States on the reverse.