Iran is subdivided into 31 provinces (in Persian: استان, Ostān). These are administered from a central city, usually the largest city in the province. Provincial governors (in Persian: استاندار, Ostāndār) are appointed by the Minister of the Interior. Each province (Ostān) is divided into departments (Shahrestān), which is divided into townships (Bakhsh), which include about ten cities (Shahr). The cities are subdivided into villages or districts (dehestān) it is the smallest administrative unit. In 2005, Iran had 324 counties, 865 cantons, 982 towns and 2,378 villages.

The administrative structure of Iran changes periodically. At the beginning of the twentieth century, Iran has twelve provinces. In 1950, the territorial division was reorganized into ten provinces. Several provinces are then created and in 1986, they are 24. In the 1990s, the provinces of Ardebil, Golestan, Qazvin and Qom are added. In 2004, Khorassan Province is divided into three provinces: Northern Khorasan, Southern Khorasan and Khorassan Ravazi. In 2010, the region of Karaj is detached from the province of Tehran to form the province of Alborz.

Tehran, with a population of around 8.8 million (2016 census), is the capital and largest city of Iran. It is an economical and cultural center, and is the hub of the country's communication and transport network.


The country's second most populous city, Mashhad, has a population of around 3.3 million (2016 census), and is capital of the province of Razavi Khorasan. Being the site of the Imam Reza Shrine, it is a holy city in Shia Islam. About 15 to 20 million pilgrims visit the shrine every year.


Isfahan has a population of around 2.2 million (2016 census), and is Iran's third most populous city. It is the capital of the province of Isfahan, and was also the third capital of the Safavid Empire. It is home to a wide variety of historical sites, including the famous Shah Square, Siosepol, and the churches at the Armenian district of New Julfa. It is also home to the world's seventh-largest shopping mall, Isfahan City Center.


The fourth most populous city of Iran, Karaj, has a population of around 1.9 million (2016 census). It is the capital of the province of Alborz, and is situated 20 km west of Tehran, at the foot of the Alborz mountain range. It is a major industrial city in Iran, with large factories producing sugar, textiles, wire, and alcohol.


With a population of around 1.7 million (2016 census), Tabriz is the fifth most populous city of Iran, and had been the second most populous until the late 1960s. It was the first capital of the Safavid Empire, and is now the capital of the province of East Azerbaijan. It is also considered the country's second major industrial city (after Tehran).


Shiraz, with a population of around 1.8 million (2016 census), is Iran's sixth most populous city. It is the capital of the province of Fars, and was also the capital of Iran under the reign of the Zand dynasty. It is located near the ruins of Persepolis and Pasargadae, two of the four capitals of the Achaemenid Empire.