Azeri people speak Azerbaijani Turkish or Azeri Turkish. The most majority of Azerbaijanis are Shi'a Muslims.
Iranian Azerbaijanis mainly live in the Northwest provinces such as: East Azerbaijan Province, West Azerbaijan Province [Eastern part of it, which is marked from the middle line of Urmiya Lake (meaning the eastern part of the median course of the Lake)], Ardabil Province, Zanjan Province, Qazvin Province, Hamadan Province (northern part of it) and also many Azeris live in Tehran (23, 16, Map1).
 
There are an estimated of 28 to 30 million Azerbaijanis in the world, but census figures are difficult to verify. A diaspora Azeri, possibly numbering in millions, is found in neighboring countries and around the world (8, 14).
The vast majority of Azeris live in Azerbaijan Republic (Approximately 8 million) and Azerbaijan of Iran. About 19 million Azeris live in Iran, mainly in the Northwestern provinces and also in Tehran.
 
The populations of Iranian Azeri Turks in Azeri dominated cities are: East Azerbaijan (3.600.000), West Azerbaijan Province [about less than 50% of the Province is Azeri; in figure it becomes about; 1.500.000, [Eastern part of the Province is Azeri’s inhabited which is historically marked from the middle line of Urmiya Lake (meaning the Eastern part of the median course of the Lake, there is a debate on this between either sides’ elites)], Ardabil province (1.250.000), Zanjan province (about 980.000), Qazvin Province (about 1.150.000), Hamadan Province (if about 50% of the province be Azeri Turks; in figure it becomes about 850.000), and about 33% of Tehran (Population of Tehran is 13.450.000) is Azeri Turks; which in figure becomes about 4.5 million (4.500.000), (7, figure 3 & 4, Graph 1& 2, Table 1).

The sum of all Azeri Turks in dominated Provinces becomes about 14 million (14.000.000). According to some nationalist Azeris; there are about 2.5 to 4.5 million Azeri Turks who are scattered in other provinces across the state and also far suburban of Tehran. If this be the case, then all population of Azeri Turks in Iran is about 18.5 million (about 25% of the State population is Azeri Turks).
While population estimates in Azerbaijan Republic are considered reliable due to regular censuses taken, the figures for Iran remain questionable. Since the early twentieth century, successive Iranian governments have always avoided publishing statistics on ethnic minorities for political gains.
 
Generally, until the Pahlavi ruling period in the twentieth century, "the identity of Iran was not exclusively Persian, but supra-ethnics". Resentment came with Pahlavi policies of making one state /one nation, and by that the minorities’ languages and cultures suppressed with brutality in local government, local areas, schools, and totally banned in the press and audio/video media. However with the advent of the Iranian Revolution in 1979, emphasis shifted away from nationalism as the new government highlighted religion (Shiism) as the main unifying factor.
 
Within the Islamic Revolutionary government there emerged an Azeri nationalist faction led by Ayatollah Kazem Shariatmadari, who advocated greater regional autonomy, 1979 AC. He wanted the constitution to be revised to include secularists and opposition parties; this was denied. On today there is some civil unrest due to the systematic policies of the Iranian government upon Azeris demands.