Tehran is the capital of Iran and Tehran Province. With a population of around 8.3 million and surpassing 14 million in the wider metropolitan area, Tehran is Iran's largest city and urban area, and the largest city in Western Asia.

In the 20th and 21st centuries, Tehran has been the subject of mass migration of people from all around Iran. The city is home to many historic mosques as well as several churches, synagogues and Zoroastrian fire temples. However, modern structures, notably Azadi Tower and the Milad Tower, have come to symbolise the city. 

Tehran is ranked 29th in the world by the population of its metropolitan area. Throughout Iran's history, the capital has been moved many times, and Tehran is the 32nd national capital of Iran. Although a variety of unofficial languages are spoken, roughly 99% of the population understand and speak Persian. Majority of the inhabitants of the city are Persian speakers (known by the name Pars/Fars), but there are also large populations of Kurds (Kord), Azarbaijanis (Azeri/Tork), Lurs (Lor) and Northern Iranians (Shomali). The majority of people in Tehran identify themselves as Persians. In pre-Islamic and early Islamic times, Tehran was an unimportant village and part of the area of present-day Tehran was occupied by Rey (which in the Avesta occurs in the form of Rhaga, now a part of the city of Tehran, which took over its role after the destruction of Rey by the Mongols in the early 13th century.

A plan to move the capital has been discussed many times in prior years. In 2010, the government of Iran announced that "for security and administrative reasons" the plan to move the capital from Tehran has been finalized. The Iranian Parliament named Shahroud, Esfahan and Semnan as three of main candidates to replace Tehran as the capital.