Several left-wing guerrilla groups attempting to overthrown the pro-Western regime of Shah Mohammad Reza Pahlavi were notable and active in Iran from 1971 to 1979. The groups shared a commitment to armed struggle, but differed in ideology. Most were Marxist in orientation. The largest group — People's Mujahedin of Iran — was founded as a left wing movement with the aim to overthrow Iran's cleric rule. 
 Four guerrilla organizations — the Feda'i, the pro-Tudeh Feda'i Munsh'eb, the Islamic Mujahedin and the Organization of Struggle for the Emancipation of the Working Class — are said to have "delivered the regime its coup de grace," in the street fighting of February 9–11, 1979.
 According to Ervand Abrahamian, a scholar of the subject:
 In terms of political background, the guerrillas can be divided into five groups:
 Guerrilla groups formed it is believed, because the non-armed, mass-based communist Tudeh Party was under such intense repression it was unable to function, while in the outside world guerillas Mao Zedong, General Võ Nguyên Giáp and Che Guevara were having, or had had, much success. The Iranian guerrilla strategy has been described by Abrahamian as "heroic deeds of violent resistance to break the spell of government terror".
  In a situation where there are no firm links between the revolutionary intelligentsia and the masses, we are not like fish in water, but rather like isolated fish surrounded by threatening crocodiles. Terror, repression, and absence of democracy have made it impossible for us to create working-class organizations. To break the spell of our weakness and to inspire the people into action we must resort to revolutionary armed struggle... The background of the guerrillas was overwhelming educated middle class. From 1971 to 1977 an estimated 341 of them were killed, of whom over 90% of those for whom information could be found were intellectuals.
 The event from which most historians mark the beginning of the guerrilla era in Iran was the February 8, 1971 attack on a gendarmerie post at Siahkal on the Caspian Sea. Guerillas killed three policemen and freed two previously arrested guerrillas.
 The guerrilla organizations were quite active in the first half of the 1970s.  In the two and half years from mid 1973 through 1975, three United States colonels, a Persian general, a Persian sergeant, and a Persian translator of the United States Embassy were all assassinated by guerrilla groups. In January 1976 eleven persons sentenced to death for these killings.
 By the second half of the 1970s, however, the groups were in decline, suffering from factionalism and government repression.
 By late 1978 however, the massive demonstrations, return of oppositionists from abroad, and pressure on the monarchy's security forces from the revolutionary movement revived the groups. Guerilla groups became active "both in killing Iranian military and police leaders and participating in oppositional demonstrations ... in the course of 1978 ... the Fedaiyan and the Mojahedin were able to ... become sizable movements, largely of young people."
 Islamic Nations PartyKurdistan Free Life PartyKurdistan Freedom PartyPeople's Democratic FrontUnion of Communist MilitantsWorker-communist Party of Iran – HekmatistWorker's Way