Communist Party, U.S.A., the formal organization in the United States of persons who advocate Marxism-Leninism and support the Communist movement. The goal of the party is the overthrow of capitalism, by peaceful or revolutionary means, and the establishment of a Communist society.

The first Communists appeared in the United States after the Russian Revolution of 1917. They were few in number, but their advocacy of revolution caused widespread fear and led to a series of arrests and deportations. Two competing parties were formed in 1919, the Communist Party of America and the Communist Labor Party. They merged in 1921 as the Communist Party of America (becoming the Communist Party, U.S.A., in 1940). The party remained weak until the 1930's, when the Depression caused membership to rise to about 100,000. It gained control of some labor unions and liberal organizations.

The Communist party at first opposed United States entry into World War II. After Hitler attacked the Soviet Union in 1941, however, the Communists demanded United States intervention against Germany, and later they assisted in the war effort.

After World War II many people in the United States became concerned about Communist espionage and subversion. Federal laws were enacted that virtually outlawed the Communist party. Many Communists were imprisoned, and party membership decreased.

During the 1960's, the United States Supreme Court declared many provisions of the anti-Communist laws of the previous decade unconstitutional. The party became openly active again in the 1970's.

Membership is estimated at about 15,000.