Atabeg, Atabek, or Atabey is a hereditary title of nobility of Turkic origin, indicating a governor of a nation or province who was subordinate to a monarch and charged with raising the crown prince. The first instance of the title's use was with early Seljuk Turks who bestowed it on the Persian vizier Nizam al-Mulk. It was later used in the Kingdom of Georgia, first within the Armeno-Georgian family of Mkhargrdzeli as a military title and then within the house of Jaqeli as princes of Samtskhe.

The word atabeg is a compound of the Turkic word ata, "ancestor", or "father" and the word beg or bey, "lord, leader, prince". Beg is stated in some sources as being of Iranian origin (as in the compound Baghdad from bag/beg "lord" and dad "given"). However, according to Gerhard Doerfer, the word beg may have possibly been of Turkic origin – the origin of the word still remains disputed to this day.

The title Atabeg was common during the Seljuk rule of the Near East starting in the 12th century. It was also common in Mesopotamia (Iraq). When a Seljuk prince died, leaving minor heirs, a guardian would be appointed to protect and guide the young princes. These guardians would often marry their wards' widowed mothers, thus assuming a role similar to a surrogate father's. Amongst the Turkmen tribes, as in Persia, the rank was senior to a khan.

The title Atabeg was also in use for officers in Mamluk Egypt; some of them were proclaimed sultan before the incorporation into the Ottoman Empire. After the end of Seljuk rule, the title was used only intermittently.

When describing the Atabegs of Azerbaijan, the Ildeniz (Ildegoz) dynasty, the title Atabeg-e-Azam (Great Atabeg) was used, to denote their superior standing, power and influence on the Seljuk sultans.

In Persian, the style Atabek-e-Azam was occasionally used as an alternative title for the Shah's Vazir-e-Azam (Grand Vizier), notably in 1834–35 for Mirza Abolghasem Farahani, Gha'em Magham, in 1848–51 for Mirza Mohammed Taghi Khan, Amir-e Kabir, in 1906–07 for Mirza Ali Asghar Khan, Amin-ol Soltan, and finally in 1916 for a Qajar prince, Major-General Shahzadeh Sultan 'Abdu'l Majid Mirza, Eyn-ol Douleh.

Beginning in the twelfth century the atabegs formed a number of dynasties, and displaced the descendants of the Seljukid emirs in their various principalities. These dynasties were founded by emancipated Mamluks, who had held high office at court and in camp under powerful emirs. When the emirs died, they first became stadtholders for the emirs' descendants, and then usurped the throne of their masters. There was an atabeg dynasty in Damascus founded by Toghtekin (1103–1128).

Other atabeg "kingdoms" sprang up to the north east, founded by Sokman (Sökmen), who established himself at Kaifa in Diyarbakır about 1101, and by his brother Ilghazi. The city of Mosul was under Mawdud ibn Altuntash, and was later ruled by atabegs such as Aksunkur and Zengi. Zengi became Atabeg of Mosul in 1128 and soon established himself as an independent ruler of much of northern Mesopotamia and Syria (including Aleppo).