There are about one and a half million Nomads in modern Iran, extending from the border of Turkistan to the warm waters of the Persian Gulf. Most of these tribes, the Kurds, the Lurs, the Bakhtiaris, the Guilaks (on the Caspian Coast), the Baluchis, are the original invaders who, in the first millennium BC, swept down from Central Asia and settled in various parts of the Iranian Plateau. Most the tribes of central Iran are from pure Aryan stock, while other tribes such as the Arabs of Khuzestan and Khorassan, the Turkish tribes of Quchan, the Qashqai tribes, the Shahsevan and Afshar tribes of Azarbaijan and the Turkmans are remnants of races that have passed through Iran at various periods of history.
Traditionally, there has always existed a close link in Iran between the ruling dynasty and the domination of one particular tribe or ethnic group. In the 20th century, some governments have in vain attempted to carry out national integration, or personalization, of this heterogeneous population (particularly during the reign of Reza Shah, in the hope that tribal and cultural distinctions would disappear with the economic and political development of the country.
There are many divisions and sub-divisions for each of the main tribes and tens of smaller tribes. With the expansion of education and better communications the young generation of Iranian tribes has made great progress supplying very intelligent engineers, medical men, administrators, scientists and even women doctors to serve the country.
Today there are over a hundred different tribes, each with its own dialect, picturesque dress, dwelling-place and chief. The most important tribes are as follows:
Afshars and Shahsevans
Having arrived in Iran in two waves under the Seljuks and the Mongols in 11th and 13th centuries, respectively, Afshars are pastoral nomads. They have their summer quarters on the slopes of the Sabalan Mountain at 4860 meters (Azarbaijan), between Lake Uremia and Qazvin and Hamadan, and their winter quarters are in the hot plains of Moghan, near the Caspian Coast. Some Afshar tribes are also scattered in areas between Kerman and Bandar-e Abbas in southern Iran.
Currently, an ever-increasing number of Afshars have settled down and became farmers.
Living in the northeastern Azarbaijan Province, Shahsevans were organized by Shah Abbas I in the 17th century as a militia from tribes of diverse origin. Mainly Turkish speaking, they were used to put down rebellions of other tribes. They were divided between Iranian Azarbaijan and the Russian or former Soviet Azarbaijan after the occupation of part of our country by the aggressive Russian forces during the Qajar era.

Bakhtiatis
They dwell in the high grounds of Zard Kuh Mountain (Zagros range to the west of Isfahan) extending to the south of Isfahan, and around Shahr-e Kurd, with winter quarters in Khuzestan, particularly the kinder plains around Dezful, Susa, and Ramhormoz. They are divided into two main groups, the Haft Lang and the Chahar Lang, subdivided in turn into several tribes and sub-tribes or tayefeh.

Most Bakhtiaris speak Persian or a Luri dialect, although part of the populations, concentrated in the towns and villages in the south of Khuzestan Province, speak Arabic. Their clothing, with trousers extraordinarily wide, round hat and short tunic, is reminiscent of the Arsasid (Parthian) period, 200 BC-280 AD.

Baluch tribes
Originating in Khorassan, northeastern Iran, they are scattered and live in the Mokran region far southeast of the country, a vast area from the Pakistan border to the Iranian deserts. Their language is pure Persian. Nowadays mainly settled in urban centers such as Zahedan, the Baluch tribes consist of many different smaller tribes, making their living out of camel herding and agriculture.

Guilaks
These tribes are among the most original tribes of Iran, speaking a pure Persian dialect and dwelling in the maritime provinces of Iran. Their number is dwindling, but one can still see the remnants of these stoic tribes in Talish.

Kurds

The Kurdish people of Iran occupy a vast area from the northwest borderline of Azarbaijan to the hot plain of Khuzestan. Descendants of the Indo-European tribes that arrived in Iran in the first millennium BC, they speak an Old Persian dialect and regard themselves as the descendants of the Medes. Kurds are to be found mainly in Iran, Iraq, and Turkey. 
  
Lur tribes
They are probably the most intact tribes of Iran, retaining their robustness, virility, and tall stature. They are mostly cultivators and shepherds and occupy the high grounds of Lurestan, south of Kurdestan, and Kermanshah provinces.
They thought to be a division of the ancient Kurds, both tribes being considered true descendants of the Medes. The Mamasani Lurs dwelling in western mountains of Fars form one of the most important clans.

Qashqais
These Turkish-speaking tribesmen are historically the most important political leverage, dwelling among the high mountains of Fars Province. Traditionally, they wintered on pastures in the foothills of the Zagros to south and west of Shiraz, near the Persian Gulf, and moved north to the mountains in the spring. Their dress is almost the same as that of the Bakhtiaris, except for the hat, which resembles Napoleonic headgear.
  
Turkmans
They descend from the Mongols who arrived in Iran very early on, in the 11th century AD, and are powerfully built, with high cheekbones and slanting eyes. They live in the northeast of the country, north of Khorassan and east of Mazandaran. They dwell on the vast flat lands of Turkmansahra, which is situated between the Caspian Coast and the southern mountains. Currently, they constitute the most active agriculturists and fishermen of the region.
                                                                                                                                                                        (Source: Iran Traveling Center)