The oldest human being relics in Iran dates back to almost one million years ago. It’s been discovered in the basin of Atrakrud in northeastern part of the country. Around 12000 years ago the cavemen started to descend and spread in the vast plains of the Iranian plateau.

At least since 9000 years ago agricultural communities started on the Iranian plateau. Domestic animals were raised, and producing painted pottery and polished stone implements started to be prevailed. One can find more than one million archeological mounds in this ancient land. Sites datable to later than 3000 BC are numerous. Indo-Europeans (Aryans) began to enter the plateau of Iran around  1500 BC . The Iranian group included Medes, Persians, Parthians, Bactrians, and others. The Medes settled in western Iran (Media) about 900 BC and established their capital at Ecbatana (modern Hamadān); the Persians settled to the south of the Medes (Parsis) around 700 BC. The Medians, along with the Chaldeans, destroyed the power of neighboring Assyria. In the area of Parsis, the Achaemenid clan became overlords, and in 550 BC, their leader, Cyrus the Great, revolted against the Medes; forming an alliance  of Medes and Persians, he then established the Achaemenid Empire. Cambyses, Darius, Xerxes I, and Artaxerxes I were notable rulers of this line who penetrated Greece, Egypt, and beyond the Oxus. The Achaemenid power was centered at Susa, Ecbatana and Persepolis.

334–330 BC, Alexander the Great invaded eastward including Persia. He ended up with the collapse of  Achamenid Empire. Around 250 BC, the Parthians pushed the Macedonians out of Iran and established the new Parthian kingdom; a kings who came in contact with and then to fought the Roman Empire. Weakened by long wars with Rome, the Parthians were followed by the next dynasty, the Sassanids, which arose in the area of Fars in southwestern Iran. Wars with Rome continued and were followed by a struggle with the Byzantine Empire. The Sassanian period (AD 226–641) was one of cultural consolidation and was marked by strong economic activities.

During the first half of the 7th century AD, Islam was revealed to Prophet Mohammad and Arab warriors could overwhelm the Sassanian Empire and spread the teachings of the Islam. By the opening of the ninth century, Islamic doctrine and precepts had spread over the plateau, and local dynasties faithful to the Muslim creed emerged. 

Early in the 11th century, the Turkish Ghaznavid dynasty grasped the power, their greatest ruler was Mahmud of Ghaznī. The Ghaznavids were replaced by the Seljuks.

The Seljuk kingdom had its capital at Ray, just south of Tehrān, and stretched from the Bosporus to Chinese Turkestan could manage to enhance the character of Persian language and civilization.

In 1219, Genghis Khan (Temujin) began to invade into Iran; successive waves subdued and devastated the country. Hulagu, a grandson of Genghis, settled in Maragheh in Azerbaijan established the Il-khanid dynasty. His successors ruled from Tabriz and Sultaniya, and once again untutored invaders became converts to Islam and patrons of Persian science, learning, and arts. Rivalries within the military leadership brought about the breakdown of Il-khanid power in the second half of the 14th century.

In 1380, "Timur the Lame," (Tamerlane) began to march into the Iranian lands from the east. a renaissance of culture at Herāt (in modern Afghanistan) and other towns were started. His successors couldn’t hold the empire together. Early in the 16th century a number of smaller, local dynasties emerged all around Iran. The Safavid dynasty was the strongest. Its leaders were descendants of a spiritual head of the Sufi sect, Sheikh Safyeddin Ardebili. Safavids declared Shiism as the official religion of Iran. Shah Abbas (r.1587–1628) moved the capital to Esfahān. The Safavid period, marked by the emergence of a truly native Iranian dynasty after the lapse of centuries, was a period of general prosperity. In 1722, Esfahān fell to invading Afghans. Nadir Shah, an Afshar tribesman from the north, drove off the Afghans and in 1736 established the Afshar dynasty. By the end of the 18th century, Zand rulers who ruled in the south, were replaced by the Qajars, a Turkish tribe.

Qajar period is a time we faced the West much deeper than before. In 1906, a coalition of bazaar merchants, clerics, intellectuals, and tribal leaders forced the shah to accept a constitution. This liberal initiative was interfered by the power of the British and Russians, who controlled spheres of influence in the south and north of Iran.

The British arranged a coup and Reza Khan came to power in 1925 as Reza Shah, the first of Pahlavi dynasty. With ruthless authority, he sought to modernize Iran along the lines of Ataturk in Turkey. In 1941, suspecting him of pro-German sympathies, the British forced Reza Shah to abdicate in favor of his 21-year-old son, Muhammad Reza. British and Russian forces set up a supply line across Iran to the USSR. In April 1946, the British left, but the USSR refused to withdraw its forces. Under pressure from the United Nations (UN) and the United States, Soviet troops withdrew in December 1946.

Muhammad Mossadeq, as leader of the National Front in the national assembly (Majlis), could lead the Majlis vote to nationalize the oil industry on 1951.  In April, Mossadeq became Iran’s prime minister.  In August 1953, the still popular Mossadeq was toppled down by a US and UK backed military coup.  

After 1953, the shah began to consolidate his power. The left-wing Tudeh (Masses) Party  was suppressed. And in 1957, Savak (Iran’s security force) was formed by CIA. In practice the political dissent was not tolerated. The opposition arose against shah in the late 1970s. Islamic militants, radical students, and the middle class all joined in the revolt, until virtually the entire population turned against the shah. Following demonstrations and violent army reactions, martial law was declared in Iran's major cities in September 1978. On 16 January 1979, the shah left Iran. However, the leader of the Islamic opposition, Ayatollah Ruhollah Khomeini  who had spent 15 years in exile, first in Iraq and briefly in France, on 1 February returned to Tehran, as a result of the continued demonstrations. He quickly appointed a provisional government, which took power after a military rebellion and the final collapse of the shah's regime on 11 February. 

After a referendum on 1 April Iran was declared an “Islamic republic”. Later, the new constitution for an Islamic democracy was ratified by popular referendum in December 1979. Shah died in Egypt on 27 July 1980.

Iraq, meanwhile, took advantage of Iran's political chaos and economic disorder to revive a border dispute that had been settled in 1975 when Iranian and Iraqi representatives reached agreement on the demarcation of their frontiers. Full-scale war erupted in September 1980, when Iraq demanded sovereignty over the entire Shatt al Arab waterway. Iraqi forces invaded Iran’s territory, and captured more than 20 Iranian towns including Khorramshahr and the oil refinery center of Ābādān. Iranian forces by June 1982 could drive Iraqi soldiers out of Ābādān and Khorramshahr and from all undisputed Iranian territory. 

On 3 June 1989 Ayatollah Khomeini died of a heart attack. Over three million people attended his funeral. He was succeeded as the country's spiritual guide by Ayatollah Ali Khamenei.