Tehran is the largest city in the Middle East and is the 28th most populated city in the world with a population of 7,873,000 people. Most Iranian industries are headquartered in Tehran, including the manufacturing of automobiles, electrical equipment, military weaponry, textiles, sugar, cement, and chemical products. Tehran is also a leading center for the sale of carpets and furniture. There is an oil refinery located south of the city.

In the 20th century, Tehran faced a large migration of people from all around Iran. Today, the city contains various religious minorities, and has many historic mosques, churches, synagogues and Zoroastrian fire temples. Contemporary Tehran is a modern and expensive city featuring many skyscrapers, of which the Azadi Tower and the Milad Tower have come to be symbols of Tehran itself.

The origin of the name Tehran is unknown. Excavations place the existence of settlements in Tehran as far back as 6000 BC. Tehran was well known as a village in the 9th century, but was less well-known than the city of Rhages (Ray) which was flourishing nearby in the early era. In the 13th century, following the destruction of Ray by Mongols, many of its inhabitants escaped to Tehran. In some sources of the early era, the city is mentioned as "Rhages's Tehran" . The city is later mentioned in Hamdollah Mostowfi's Nuz'hat al-Qulub (written in 1340) as a famous village.

Don Ruy Gonzáles de Clavijo, a Castilian ambassador, was probably the first European to visit Tehran, stopping in July 1404, while on a journey to Samarkand (now in Uzbekistan) and the Mongol capital at the time. At this time, the city of Tehran was unwalled.

Tehran became a residence of the Safavid rulers in the 17th century. Tahmasp I built a bazaar and a wall around the city, but it somewhat fell out of favor after Abbas I turned sick when he was passing the city to go to a war with the Uzbeks.

In the early of 18th century, Karim Khan Zand ordered a palace, a harem, and a government office to be built in Tehran, possibly to declare the city his capital, but later moved his government to Shiraz. Tehran finally became the capital of Iran in 1795, when the Qajar king Agha Mohammad Khan was crowned in the city. It remains the capital to this day.

During World War II, British and Soviet troops entered the city. Tehran was the site of the Tehran Conference in 1943, attended by U.S. President Franklin D. Roosevelt, British Prime Minister Winston Churchill, and Soviet Premier Joseph Stalin.

Following the war, the city's older landmarks suffered under the rule of Mohammad Reza Shah. The Shah believed that ancient buildings such as large parts of the Golestan Palace, Takieh-ye Dowlat, the Toopkhaneh Square, the magnificent city fortifications and the old citadel among others should not be part of a modern city. They were systematically destroyed and modern 1950s and 1960s buildings were built in their place. Tehran bazar was divided in half and many historic buildings were destroyed in order to build wide straight avenues in the capital. Many excellent examples of Persian Gardens also became targets to new construction projects. The decision to carry these out is presently largely seen as a foolish mistake that hurt the visual fabric and the cultural identity of the city beyond repair. Apartment blocks were introduced in this period.

During the 1980–88 Iran–Iraq War, Tehran was the scene of repeated Scud missile attacks and air strikes against random residential and industrial targets within the city, resulting in thousands of civilian casualties. Material damage was repaired soon after each strike. Tehran attracted war refugees by the millions.

After the war, cheap Soviet-style apartments multiplied throughout the city without any plan. At present, little is left of Tehran's old quarters. Instead, modern high-rise buildings dominate the city's skyline and new modern apartments have and are replacing the few remaining old houses at a rapid pace. Tehran-style home architecture has almost vanished completely. This is often referred to as "Tehran Identity Disaster".

Tehran is also home to many grand mansions in the north of the city.(Farmanieh, Zaferanieh, Niavaran, etc)

Tehran is the economic centre of Iran. About 30% of Iran’s public-sector workforce and 45% of large industrial firms are located in Tehran and almost half of these workers work for the government. Most of the remainder of workers are factory workers, shopkeepers, laborers, and transport workers. Few foreign companies operate in Tehran because of the Islamic government and its poor relations with the west. But before the Islamic revolution many western companies were active in this region. Today many modern industries of this city include the manufacturing of automobiles, electronics and electrical equipment, weaponry, textiles, sugar, cement, and chemical products. It is also a leading center for the sale of carpets and furniture. There is an oil refinery near Ray, south of the city. Tehran has four airports, including Mehrabad International Airport, Imam Khomeini International Airport, Ghal'eh Morghi airfield and Doshan Tapeh airbase. The country's largest paint manufacturer Rangsazi Iran has its center of operations based in Tehran.

Tehran relies heavily on private cars, buses, motorcycles, and taxis, and is one of the most car-dependent cities in the world. The Tehran Stock Exchange, which is a full member of the Federation Internationale des Bourses de Valeurs (FIBV) and a founding member of the Federation of Euro-Asian Stock Exchanges, has been one of the world's best performing stock exchanges in recent years.