Tehran is the most populous city and capital of Iran, the capital of Tehran Province and Tehran County. The city had a population of 9,039,000 in 1401 and, according to the 2018 United Nations estimate, is the thirty-fourth[6][7] most populous city in the world and the most populous city in Western Asia. The metropolis of Tehran is also the second most populous metropolis in the Middle East.

The history of life in Tehran dates back to the Neolithic period, and archaeological excavations in Tehran have led to the discovery of 7,000-year-old human skeletons and stone tools. In the early 7th century, with the destruction of the city of Rey and the migration of its people to Tehran, the knowledge of trade, construction, and citizenship of the Rey people was transferred to Tehran and contributed to its development. During the Safavid era, Tehran's importance increased greatly, but the source of the city's prosperity and progress goes back to its capital. Agha Mohammad Khan Qajar, the founder of the Qajar dynasty, who had finally succeeded in capturing Tehran after many attempts, declared Tehran the capital on Nowruz in 1165, after years of war with the Zand dynasty and claimants to the throne. Tehran's transformation from an ordinary city to a modern capital began during the Pahlavi era. During the Pahlavi era, state affairs were centralized in the capital and the number of government employees in the city increased rapidly; during this period, Tehran also assumed administrative duties in addition to its political and commercial duties. With the 1979 revolution and the beginning of the Iran-Iraq War, there was no development in Tehran for nearly a decade, and after the end of this period, the development of the Iranian capital continued and Tehran became the center of population reception in Iran.

Tehran is the economic center of Iran and is considered the country's first industrial region, but international economic activities do not play a significant role in the number of its employees. According to statistics from 2016, Tehran's share in Iran's total GDP is 21% and, with half of the country's industrial sector, it plays an important role in Iran's economy. The city is considered one of the most important tourist centers in Iran and has a collection of tourist attractions that include its palaces and museums. The Azadi Tower is the symbol of Tehran, and the Cyrus the Great Charter was first unveiled here. Milad Tower is another symbol of Tehran and the tallest tower in Iran. By hosting the 1974 Asian Games, Tehran was the first city in the Middle East to host the Asian Games, and the Azadi Sports Complex, one of the most advanced of its time, opened simultaneously with these games on September 1, 1974.

Administratively, Tehran is divided into 22 regions and 122 urban districts and includes the cities of Tajrish and Rey. The city is administered by the Tehran Municipality. The mayor of Tehran is elected by the Tehran City Council, which oversees the performance of the municipality and legislates for the city's administration. In 1968, the first comprehensive plan for Tehran was prepared with a 25-year horizon and was the responsibility of Abdolaziz Farmanfarmaian and Victor Gruen, which was one of the most important legal foundations for the development of Tehran. As a political and administrative center, the most important governmental and judicial institutions of Iran, such as ministries and the Islamic Consultative Assembly, in which Tehran has 30 representatives, are located in this city. The city has two airports, Imam Khomeini International Airport and Mehrabad Airport, which are among the busiest airports in Iran.

In terms of natural ruggedness, Tehran is divided into two regions: the plains and the Alborz foothills, and its current area extends from an altitude of 900 to 1800 meters above sea level. Tehran has a semi-arid climate. In most years, the winter season provides half of Tehran's total annual rainfall, and the summer season is the driest season in Tehran. Tehran is a city with a diverse ethnic group but has a small foreign population. As the largest Persian-speaking city in the world, the majority of Tehran's population is Persian-speaking, and most of the city's population is officially Muslim and Twelver Shia. Other religious communities in Tehran include Sunnis, Baha'is, Zoroastrians, Christians, and Jews.