Prohibition in the United States is repealed for beer of no more than 3.2% alcohol by weight, eight months before the ratification of the Twenty-first Amendment to the United States Constitution. (Now celebrated as National Beer Day in the United States.)

The Prohibition era was the period from 1920 to 1933 when the United States prohibited the production, importation, transportation, and sale of alcoholic beverages. The alcohol industry was curtailed by a succession of state legislatures, and Prohibition was formally introduced nationwide under the Eighteenth Amendment to the United States Constitution, ratified on January 16, 1919. Prohibition ended with the ratification of the Twenty-first Amendment, which repealed the Eighteenth Amendment on December 5, 1933.

Beer is an alcoholic beverage produced by the brewing and fermentation of starches from cereal grain—most commonly malted barley, although wheat, maize (corn), rice, and oats are also used. The grain is mashed to convert starch in the grain to sugars, which dissolve in water to form wort. Fermentation of the wort by yeast produces ethanol and carbonation in the beer. Beer is one of the oldest and most widely consumed alcoholic drinks in the world, and one of the most popular of all drinks. Most modern beer is brewed with hops, which add bitterness and other flavours and act as a natural preservative and stabilising agent. Other flavouring agents, such as gruit, herbs, or fruits, may be included or used instead of hops. In commercial brewing, natural carbonation is often replaced with forced carbonation.

The Twenty-first Amendment to the United States Constitution repealed the Eighteenth Amendment to the United States Constitution, which had mandated nationwide prohibition on alcohol. The Twenty-first Amendment was proposed by the 72nd Congress on February 20, 1933, and was ratified by the requisite number of states on December 5, 1933. It is unique among the 27 amendments of the U.S. Constitution for being the only one to repeal a prior amendment, as well as being the only amendment to have been ratified by state ratifying conventions.