The Japanese Communist Party (JCP; Japanese: 日本共産党, Nihon Kyōsan-tō) is a political party in Japan and one of the largest non-governing communist parties in the world. The JCP advocates for the establishment of a society based on scientific socialism, communism, democracy, peace, and antimilitarism. It proposes to achieve its objectives by working within a democratic framework while struggling against what it describes as "imperialism and its subordinate ally, monopoly capital". The party does not advocate violent revolution, instead, it proposes a "democratic revolution" to achieve "democratic change in politics and the economy" and "the complete restoration of Japan's national sovereignty", which it sees as being infringed upon by Japan's security alliance with the United States, although it firmly defends Article 9 of the Japanese Constitution and aims to dissolve the Japan Self-Defense Forces, which it considers unconstitutional, due to its opposition of the re-militarization of Japan.

The JCP is one of the largest non-ruling communist parties in the world, with approximately 270,000 members belonging to 18,000 branches. In the wake of the Sino-Soviet split, the party began to distance itself from the Eastern Bloc, especially from the Soviet Union. After the dissolution of the Soviet Union, the JCP released a press statement titled "We welcome the end of a party which embodied the historical evil of great power chauvinism and hegemonism", while at the same time criticizing Eastern European countries for abandoning socialism, describing it as a "reversal of history". Consequently, the party did not suffer an internal crisis as a result of the Soviet Union's collapse in 1991, nor has it considered disbanding or changing its name or fundamental objectives, as many other communist parties have done.

The JCP polled 11.3% of the vote in 2000, 8.2% in 2003, 7.3% in 2005, 7.0% in 2009, and 6.2% in 2012. These results seemed to indicate a trend of declining support, but the party won 21 seats in 2014, up from eight in the previous general election, as the JCP received 7,040,130 votes (13.3%) in the constituency section and 6,062,962 (11.37%) in the party lists. This continued a new wave of support that was also evident in the 2013 Tokyo prefectural election in which the party doubled its representation. Fighting on a platform directly opposed to neoliberalism, the Trans-Pacific Partnership, attempts to rewrite the constitution, United States Forces Japan, and nuclear power, the JCP tapped into a minority current that seeks an alternative to Japan's rightward direction. Following the 2016 Japanese House of Councillors election, the party holds 13 seats in the House of Councillors. After the 2017 Japanese general election, the party held 12 seats in the House of Representatives, and since the 2021 Japanese general election, it holds 10 seats.