The majority of the population of Iran (approximately 80%) consists of Iranian peoples. The largest groups in this category include Persians, mostly referred to as Fars (who form 61% of the Iranian population) and Kurds (who form 10% of the Iranian population), with other communities including Semnanis, Larestanis, Gilakis, Laks, Mazandaranis, Lurs, Tats, Talysh and Baloch.

Turkic peoples constitute of 16% of the population, the largest group being the Azerbaijani. They are the second largest ethnicity in Iran. Other Turkic groups include the Turkmen, Afshar, Qashqai, Khorasani Turks, Shahsevan, Khalaj and Kazakhs peoples.

Arabs account for about 2% of the Iranian population. The remainder, amounting to about 1% of Iranian population, consists of a variety of minor groups, mainly comprising Iranian Iraqis, Iranian Assyrians, Iranian Jews, Iranian Armenians, Iranian Georgians, Circassians and Mandaeans.

In addition to its ethnic diversity, Iranian society is also not uniform in terms of religion, and some ethnic groups are both Shia and Sunni. The largest number of Shia Muslims come from the Gilaki, Mazandarani, Fars, and Lor ethnic groups, followed by the Azerbaijanis. The largest number of Sunni Muslims is from the Turkmen and Baloch ethnic groups. The Kurds and Larestanis show a more balanced distribution between the two sects, with approximately half of each being Shia and the other half Sunni.

In Iranian society, there is a prevalent sense of social cohesion in which the various ethnic groups of the country, including the Luristanis, Mazandaranis, Kurdistanis, Azerbaijanis, Baluchistanis and Semnanis, are not considered minorities, but are instead regarded as integral parts of the majority of the Iranian population.

At the beginning of the 20th century, Iran had a total population of just below 10 million, with an approximate ethnic composition of: 6 million Persians (40%), 2.5 million Azeris (25%), 1.2 million Kurds and Baluchs each (12% each).

Many of the traditional tribal groups have become urbanized and culturally assimilated during the 19th and 20th centuries, so that ethnic identity in many cases is less than clear-cut. There have also been considerable intermarriage rates between certain groups, and nearly all groups are fluent in Persian, in many cases marginalizing their traditional native tongue. Some groups may identify with their status as "ethnic minority" only secondarily, or cite multiple ethnic affiliation.

The Semnani people are a Caspian people part of the greater Iranian peoples who primarily live in northern Iran and speak the Semnani language. They inhabit the province of Semnan, east of Tehran. Today, the majority of Semnanis speak Persian as secondary language.