The Red Purge was an anticommunist movement in occupied Japan from the late 1940s to the early 1950s. Carried out by the Japanese government and private corporations with the aid and encouragement of the Supreme Commander for the Allied Powers (SCAP), the Red Purge saw tens of thousands of alleged members, supporters, or sympathizers of left-wing groups, especially those said to be affiliated with the Japanese Communist Party, removed from their jobs in government, the private sector, universities, and schools. The Red Purge emerged from rising Cold War tensions and the Red Scare after World War II, and was a significant element within a broader "Reverse Course" in Occupation policies. The Red Purge reached a peak following the outbreak of the Korean War in 1950, began to ease after General Douglas MacArthur was replaced as commander of the Occupation by General Matthew Ridgway in 1951, and came to a final conclusion with the end of the Occupation in 1952.

The Japanese Communist Party is a communist party in Japan. Founded in 1922, it is the oldest political party in the country. It has 270,000 members as of 2020, making it one of the largest non-governing communist parties in the world. The party is chaired by Tomoko Tamura, who replaced longtime leader Kazuo Shii in January 2024.