The Communist Party USA, officially the Communist Party of the United States of America (CPUSA), is a far-left communist party in the United States established in 1919 after a split in the Socialist Party of America following the Russian Revolution.

The history of the CPUSA is closely related to the American labor movement and communist parties worldwide. Initially operating underground due to the Palmer Raids starting in the First Red Scare, the party was influential in American politics in the first half of the 20th century and played a prominent role in the labor movement from the 1920s through the 1940s, becoming known for opposing racism and racial segregation after sponsoring the defense for the Scottsboro Boys in 1931. Its membership increased during the Great Depression, and they played a key role in the Congress of Industrial Organizations. The CPUSA subsequently declined due to events such as World War II, the beginning of the Cold War, the second Red Scare, and the influence of McCarthyism. Its opposition to the Marshall Plan and the Truman Doctrine were unpopular, with its endorsed candidate Henry A. Wallace under-performing in the 1948 presidential election. Its support for the Soviet Union increasingly alienated it from the rest of the left in the United States in the 1960s.

The CPUSA received significant funding from the Soviet Union and crafted its public positions to match those of Moscow. The CPUSA also used a covert apparatus to assist the Soviets with their intelligence activities in the United States and utilized a network of front organizations to shape public opinion. The CPUSA opposed glasnost and perestroika in the Soviet Union and as a result major funding from the Communist Party of the Soviet Union ended in 1989.