The Tudeh Party of Iran is an Iranian Marxist–Leninist communist party. Formed in 1941 with Soleiman Mirza Eskandari as its leader, the organization held significant influence in its early years and played an important role during Mohammad Mosaddegh's campaign to nationalize the Anglo-Persian Oil Company, as well as throughout his term as prime minister. From the Iran crisis of 1946 onwards, Tudeh became a pro-Soviet organization and remained prepared to carry out the dictates of the Soviet leadership in Moscow, even if it meant sacrificing Iranian political independence and sovereignty. The crackdown that followed the 1953 coup against Mosaddegh is said to have "destroyed" the party, although a small part of it survived. The party still exists but has remained much weaker on account of being banned in Iran and mass arrests by the Islamic Republic in 1982, as well as the executions of political prisoners in 1988. Tudeh identified itself as the historical successor of the Communist Party of Persia.

The Tudeh Party is retroactively described in conflicting ways, sometimes as "Stalinist", or as a more traditional communist party that supported the Soviet Union while also adopting nationalism to appeal more to Iranians. It is also sometimes described simply as "leftist" or even "left-leaning" by other sources.

The history of the communist movement in Iran dates back to the late 19th century, when Marxism was first introduced to the nation's intellectual and working classes as a result of the rapid growth of industry and the subsequent transformation of the country's economy from a feudalistic system into a capitalistic one. Being close to the Soviet Union and the Caucasus, northern Iran became the primary center of underground Marxist and social democrat political activity, and many such groups came into being over the years.

The Communist Party of Iran was founded in June 1920 in Bandar-e Anzali, in the province of Gilan, as a result of the first congress of Iranian social democrats. Haydar Khan Amo-oghli, who was one of the leaders of the Constitutional Revolution of Iran, became the national secretary of the new party. At the same time, Mirza Kuchik Khan, another major leader of the Constitutional Revolution and also the leader of the revolutionary Jungle "Jangali" Movement (Foresters' Movement), established the Socialist Soviet Republic of Gilan with the assistance of the Red Army of the Soviet Union.

With the defeat of both the newly formed Soviet Republic of Gilan and the Communist Party, communist and social democrat activity once again went underground. In the early 1920s the Qajar dynasty finally collapsed, and Reza Shah ascended to the throne in 1925, establishing the Pahlavi dynasty. The new Shah introduced many reforms, such as limiting the power of the Shia clergy, but also in turn established an authoritarian dictatorship.

In 1929–30, the party organized strikes in an Isfahan textile mill, the Mazandaran railways, Mashhad carpet workshops, and most importantly, in the British-owned oil industry. The government cracked down heavily and circa 200 communists were arrested; 38 were incarcerated in Qasr Prison in Tehran. Along with the Stalin purges, which took a heavy toll on Iranian communist exiles living in the Soviet Union, these arrests meant the Communist Party of Iran "ceased to exist for all practical purposes outside the walls of Qasr."

The British-Soviet Allied invasion of 1941–42 resulted in the end of Reza Shah's reign and his forced exile to South Africa. Many political prisoners subsequently received general amnesty by his son and successor Mohammad Reza Pahlavi, and under this new atmosphere, nationalist and socialist groups once again flourished. Members of the Marxist "Group of the 53 members" comprised a portion of these political prisoners. In Iran's post-Reza Shah era, the latter became a component of Soviet strategy, interests, and plans. Following their release, some of the "Group of the 53 members" including Iraj Iskandari met with a Soviet representative at the residence of Soleiman Eskandari to form the Hezb-e Tudeh-ye Iran ("the Party of Iranian masses"), a Marxist–Leninist party appealing to the broad masses. They founded the Tudeh party on 29 September 1941, electing Soleiman Eskandari as party president.

Initially the party was intended to be "a liberal rather than a radical party", with a platform stressing the importance of "constitutional" and "individual rights", protecting "democracy" and "judicial integrity" from fascism, imperialism, and militarism. "At Soleiman Eskandari's urging", the party initially attempted to appeal to non-secular masses by barring women from membership, organizing Moharram processions, and designating "a special prayer room in its main clubhouse." This orientation did not last and the party moved "rapidly to the left" within months of its founding.