The Iranian Revolution (Persian: انقلاب ایران, Enqelâb-e Irân [ʔeɴɢeˌlɒːbe ʔiːɾɒːn]), or the Islamic Revolution (انقلاب اسلامی, Enqelâb-e Eslâmī), refers to a series of events that culminated in the overthrow of the Pahlavi dynasty in 1979. It led to the replacement of the Imperial State of Iran by the present-day Islamic Republic of Iran, as the monarchical government of Mohammed Reza Pahlavi was superseded by the theocratic government of Ruhollah Khomeini, a religious cleric who had headed one of the rebel factions. The ouster of Pahlavi, the last Shah of Iran, formally marked the end of Iran's historical monarchy.

After the 1953 Iranian coup d'état, Pahlavi aligned Iran with the Western Bloc and cultivated a close relationship with the United States in order to consolidate his power as an authoritarian ruler. Relying heavily on American support amidst the Cold War, he remained the Shah of Iran for 26 years after the coup, effectively keeping the country from swaying towards the influence of the Eastern Bloc and the Soviet Union. Beginning in 1963, Pahlavi implemented a number of reforms aimed at modernizing Iranian society, in what is known as the White Revolution. In light of his continued vocal opposition to the modernization campaign after being arrested twice, Khomeini was exiled from Iran in 1964. However, as major ideological tensions persisted between Pahlavi and Khomeini, anti-government demonstrations began in October 1977, eventually developing into a campaign of civil resistance that included elements of secularism and Islamism. In August 1978, the deaths of between 377 and 470 people in the Cinema Rex fire — claimed by the opposition as having been orchestrated by Pahlavi's SAVAK — came to serve as a catalyst for a popular revolutionary movement across all of Iran, and large-scale strikes and demonstrations paralyzed the entire country for the remainder of that year.

On 16 January 1979, Pahlavi left the country and went into exile as the last Iranian monarch, leaving behind his duties to Iran's Regency Council and Shapour Bakhtiar, the opposition-based Iranian prime minister. On 1 February 1979, Khomeini returned to Iran, following an invitation by the government; several thousand Iranians gathered to greet him as he landed in the capital city of Tehran. By 11 February 1979, the monarchy was officially brought down and Khomeini assumed leadership over Iran while guerrillas and rebel troops overwhelmed Pahlavi loyalists in armed combat. Following the March 1979 Islamic Republic referendum, in which 98% of Iranian voters approved the country's shift to an Islamic republic, the new government began efforts to draft the present-day Constitution of the Islamic Republic of Iran; Khomeini emerged as the Supreme Leader of Iran in December 1979.

The success of the Iranian Revolution was met with surprise throughout the world, and was considered by many to be unusual in nature: it lacked many of the customary causes of revolutionary sentiment (e.g., defeat in war, a financial crisis, peasant rebellion, or disgruntled military); occurred in a country that was experiencing relative prosperity; produced profound change at great speed; was massively popular; resulted in the massive exile that characterizes a large portion of today's Iranian diaspora; and replaced a pro-Western secular and authoritarian monarchy with an anti-Western Islamist theocracy that was based on the concept of Velâyat-e Faqih (or Guardianship of the Islamic Jurist), straddling between authoritarianism and totalitarianism. In addition to these, the Iranian Revolution sought the spread of Shia Islam across the Middle East through the ideological tenets of Khomeinism — particularly as a means of uprooting the region's status quo, which favoured Sunni Islam. After the consolidation of Khomeinist factions, Iran began to back Shia militancy across the region in an attempt to combat Sunni influence and establish Iranian dominance within the Arab world, ultimately aiming to achieve an Iranian-led Shia political order.