The Seljuks were a branch of the Oghuz Turks who came from the Central Asian steppe. In the first half of the 11th century they established control over Iran; gains around and after 1037 mark the founding of an independent state. Their relationship with the Abbasid caliphate in Baghdad created a balance that kept military power with the Turkic dynasty and religious legitimacy with the caliph.

The state's impact was not only military. The administrative order associated with the vizier Nizam al-Mulk — its tax and land system and its network of madrasas — became a model for later Turco-Islamic states. The Seljuks also opened the door to Anatolia: after Manzikert in 1071, the westward settlement of Turkic populations began a long-term demographic and political transformation of the region — the Anatolian Seljuks and later principalities continued this process.

The dynasty's founding dates and borders are given differently across sources; the term "Great Seljuk" is used to distinguish it from the Anatolian branch. The state fragmented in the 12th century, but the administrative and cultural traditions it set lasted much longer.