|تهران بزرگ · Greater Tehran|
|• Mayor||Pirouz Hanachi|
|• City Council Chairman||Mohsen Hashemi Rafsanjani|
|• Capital city||1,552 km2 (599 sq mi)|
|• Urban||2,325 km2 (898 sq mi)|
|• Metro||8,230 km2 (3,180 sq mi)|
|Elevation||900 to 1,830 m (2,952 to 6,003 ft)|
|• Density||11,800/km2 (31,000/sq mi)|
|• Population Rank in Iran||1st|
|Time zone||UTC+03:30 (IRST)|
|• Summer (DST)||UTC+04:30 (IRDT)|
|Area code(s)||(+98) 021|
Tehran or Teheran (/ - , -/,; Persian: تهران Ťehrân [tehˈɾɒːn] (listen)) is the capital of Iran and Tehran Province. With a population of around 13.2 million in the city and 23 million in the larger metropolitan area of Greater Tehran, Tehran is the most populous city in Iran and in West Asia  and has the largest metropolitan area in the Middle East. It is ranked 9th in the world in terms of metropolitan population.
In the Classical era, part of the territory of present-day Tehran was occupied by Rhages, a prominent Median city. It was subject to destruction through the medieval Arab, Turkic, and Mongol invasions. Its modern-day inheritor remains as an urban area absorbed into the metropolitan area of Greater Tehran.
Tehran was first chosen as the capital of Iran by Agha Mohammad Khan of the Qajar dynasty in 1786, in order to remain within close reach of Iran's territories in the Caucasus, before being separated from Iran as a result of the Russo-Iranian Wars, and to avoid the vying factions of the previously ruling Iranian dynasties. The capital has been moved several times throughout history, and Tehran is the 32nd national capital of Persia. Large-scale demolition and rebuilding began in the 1920s, and Tehran has been a destination for mass migrations from all over Iran since the 20th century.
Tehran is home to many historical collections, including the royal complexes of Golestan, Sa'dabad, and Niavaran, where the two last dynasties of the former Imperial State of Iran were seated. Tehran's most famous landmarks include the Azadi Tower, a memorial built under the reign of Mohammad Reza Shah of the Pahlavi dynasty in 1971 to mark the 2,500th year of the foundation of the Imperial State of Iran, and the Milad Tower, the world's sixth-tallest self-supporting tower which was completed in 2007. The Tabiat Bridge, a newly built landmark, was completed in 2014.
The majority of the population of Tehran are Persian-speaking people, and roughly 99% of the population understand and speak Persian, but there are large populations of other ethno-linguistic groups who live in Tehran and speak Persian as a second language.
Tehran has an international airport (Imam Khomeini Airport), a domestic airport (Mehrabad Airport), a central railway station, the rapid transit system of Tehran Metro, a bus rapid transit system, trolleybuses, and a large network of highways.
There have been plans to relocate Iran's capital from Tehran to another area, due mainly to air pollution and the city's exposure to earthquakes. To date, no definitive plans have been approved. A 2016 survey of 230 cities by consultant Mercer ranked Tehran 203rd for quality of life. According to the Global Destinations Cities Index in 2016, Tehran is among the top ten fastest growing destinations.
October 6 is marked as Tehran Day based on a 2016 decision by members of the City Council, celebrating the day when the city was officially chosen as the capital of Iran by the Qajar dynasty back in 1907.
There are various theories pertaining to the origin of the name Tehran. One plausible theory is that the word "Tehran" is derived from Tiran/Tirgan, "The Abode of Tir" (Tir being the Zoroastrian deity equivalent to the Greek deity Hermes or the Roman Deity Mercury). The ancient Parthian town of Tiran was a neighbour to the town of Mehran ("The Abode of Mehr/Mithra", the Zoroastrian sun god). Both of these were mere villages in the suburbs of the great city of Ray/Rhages. Mehran is still extant and forms a residential district inside the Greater Tehran, as is also Ray—which forms the southern suburbs of Tehran. Another theory is that Tehran means "a warm place", as opposed to "a cool place" (e.g. Shemiran)—a cooler district in northern Tehran. Some current texts in this regard claim that the word Tehran in Persian means "warm mountain slope" (دامنه گرم). The official City of Tehran website says that "Tehran" comes from the Persian words "Tah" meaning "end or bottom" and "Ran" meaning "[mountain] slope"—literally, bottom of the mountain slope. Given Tehran's geographic position at the bottom of the slope of the Alborz Mountains, this appears to be the most plausible explanation of the origin of the name of the city (دامنه ی بین دو کوه).
The settlement of Tehran dates back over 7,000 years.