The Communist Party of Australia (CPA), known as the Australian Communist Party (ACP) from 1944 to 1951, was an Australian political party founded in 1920. The party existed until roughly 1991, with its membership and influence having been in a steady decline since its peak in 1945. Like most communist parties in the west, the party was heavily involved in the labour movement and the trade unions. Its membership, popularity and influence grew significantly during most of the interwar period before reaching its climax in 1945, where the party achieved a membership of slightly above 22,000 members. Although the party did not achieve a federal MP, Fred Paterson was elected to the Parliament of Queensland (for Bowen) at the 1944 state election. He won re-election in 1947 before the seat was abolished. The party also held office in over a dozen local government areas across New South Wales and Queensland.

After nineteen years of activity, the CPA was formally banned on 15 June 1940 under the relatively new Menzies government (1939–1941). The party was banned under the National Security (Subversive Associations) Regulations 1940. Two-and-a-half years later, the party was again a lawful organisation. When the party contested the federal election eight months later, it received its biggest vote total. Getting a total of 81,816 votes (1.93–2.00%), the party received over 20,000 in Victoria and Queensland, and over 19,000 in New South Wales. It was the party's biggest vote total since the 1934 federal election. However, by the late 1960s the party fell into single digit numbers before a brief spike in the mid 1970s. By the mid to late 1980s the party was effectively stagnant and the party was soon dissolved. To the present, the party is the fourth-oldest political party in Australian political history since Federation, lasting for 70 years, 122 days.