Iran, officially the Islamic Republic of Iran, country in southwestern Asia, located on the northeastern shore of the Persian Gulf. One of the world's most mountainous countries, Iran contains Mount Damāvand, the highest peak in Asia west of the Himalayas. The country’s population, while ethnically and linguistically diverse, is almost entirely Muslim. For centuries, the region has been the center of the Shia branch of Islam (see Shia Islam). Iran ranks among the world’s leaders in its reserves of oil and natural gas. As is the case in other countries in the petroleum-rich Persian Gulf region, the export of oil has dominated Iran’s economy since the early 20th century.

In the 6th century bc the territory of present-day Iran was the center of the Persian Empire, the world’s preeminent power at that time. For more than 2,000 years, the region’s inhabitants have referred to it by the name Iran, derived from the Aryan tribes who settled the area long ago. However, until 1935, when the Iranian ruler demanded that the name Iran be used, the English-speaking world knew the country as Persia, a legacy of the Greeks who named the region after its most important province, Pars (present-day Fārs). Iran was a monarchy ruled by a shah, or king, almost without interruption from 1501 until 1979, when a yearlong popular revolution led by the Shia clergy culminated in the overthrow of the monarchy and the establishment of an Islamic republic.