The Seljuk Empire or the Great Seljuq Empire[was a high medieval Turko-Persian Sunni Muslim empire, originating from the Qiniq branch of Oghuz Turks. At its greatest extent, the Seljuk Empire controlled a vast area stretching from western Anatolia and the Levant to the Hindu Kush in the east, and from Central Asia to the Persian Gulf in the south.

The Seljuk empire was founded by Tughril Beg (990–1063) and his brother Chaghri Beg (989–1060) in 1037. From their homelands near the Aral Sea, the Seljuks advanced first into Khorasan and then into mainland Persia, before eventually capturing Baghdad and conquering eastern Anatolia. Here the Seljuks won the battle of Manzikert in 1071 and conquered most of Anatolia from the Byzantine Empire, which became one of the reasons for the first crusade (1095-1099). From c. 1150-1250, the Seljuk empire declined and was invaded by the Mongols around 1260. The Mongols divided Anatolia into emirates. Eventually one of these, the Ottoman, would conquer the rest.

Seljuk gave his name to both the empire and the Seljuk dynasty. The Seljuks united the fractured political landscape of the eastern Islamic world and played a key role in the first and second crusades. Highly Persianized in culture and language, the Seljuks also played an important role in the development of the Turko-Persian tradition, even exporting Persian culture to Anatolia. The settlement of Turkic tribes in the northwestern peripheral parts of the empire, for the strategic military purpose of fending off invasions from neighbouring states, led to the progressive Turkicization of those areas.