Tehran (Persian: تهران‎ Tehrān), sometimes spelled Teheran, is the capital of Iran and Tehran Province. With an estimated population of 8,429,807; (7,711,230 - in 2,267,892 households - as of the 2006 census) it is also Iran's largest urban area and city, the largest city in Western Asia, one of the largest in Southern Asia, and the 19th largest city globally.

In the 20th century, Tehran was subject to mass-migration of people from all around Iran. The city is home to many historic mosques, churches, synagogues and Zoroastrian fire temples. Contemporary Tehran is a modern city featuring many structures, of which the Azadi (Freedom) Tower and the Milad Tower have come to be symbols of Tehran itself. In 2008 Tehran was the least expensive capital in the world and the second-least expensive city globally based on the cost-of-living index presenting the best value for money in the world. Globally it stands 19th by city population, 56th by the size of its GDP and 29th by the population of its metropolitan area. Throughout Iran's history, the capital city has been relocated many times, with Tehran being the 32nd national capital of Iran. Persian is the city's native tongue, with roughly 98% of the population able to speak and understand it. The majority of people in Tehran identify themselves as Persians. In pre-Islamic and early Islamic times, Tehran was called Ray (which in the Avesta occurs in the form of Ragha).