The Communist Party of Saudi Arabia was a pro-Soviet Marxist-Leninist party that existed from 1975 until the early 1990s. Its roots lay in the labor movement of the 1950s in the oil-producing Eastern Province. The history of this province is a hitherto almost unknown aspect of modern Saudi history, Arab Marxism, and the broader Cold War. The Saudi Communist Party helped to launch an uprising in 1979 in the Eastern Province and was particularly active in propagating its ideas throughout the 1980s as the Soviet Union and Saudi Arabia fought a proxy war in Afghanistan. Despite opposing the monarchy's use of Islam as a tool of legitimacy and a propaganda instrument against Communism in the Cold War, the party called for a common front with Islamic groups opposed to the monarchy at home. After the dissolution of the party in 1991, former party members became key actors in the reformist petitions of 1990–1991, 2003, and 2011. This article is based on fieldwork in Saudi Arabia, interviews with veteran leftists from the region, and hitherto unexamined primary sources in Arabic, German, and English, including party publications and archival sources.