The Aq Qoyunlu or the White Sheep Turkomans (Azerbaijani: Ağqoyunlular, آغ‌قویونلولار; Persian: آق‌ قویونلو) was a culturally Persianate, Sunni Turkoman tribal confederation. Founded in the Diyarbakir region by Qara Yuluk Uthman Beg, they ruled parts of present-day eastern Turkey from 1378 to 1508, and in their last decades also ruled Armenia, Azerbaijan, much of Iran, Iraq, and Oman where the ruler of Hormuz recognised Aq Qoyunlu suzerainty. The Aq Qoyunlu empire reached its zenith under Uzun Hasan.

The name Aq Qoyunlu, literally meaning "those with white sheep", is first mentioned in late 14th century sources. It has been suggested that this name refers to old totemic symbols, but according to Rashid al-Din Hamadani, the Turks were forbidden to eat the flesh of their totem-animals, and so this is unlikely given the importance of mutton in the diet of pastoral nomads. Another hypothesis is that the name refers to the predominant color of their flocks.

According to chronicles from the Byzantine Empire, the Aq Qoyunlu are first attested in the district of Bayburt south of the Pontic Mountains from at least the 1340s. In these chronicles, Tur Ali Beg was mentioned as lord of the "Turks of Amid", who had already attained the rank of amir under the Ilkhan Ghazan. Under his leadership, they besieged Trebizond, but failed to take the town. A number of their leaders, including the dynasty's founder, Qara Yuluk Uthman Beg, married Byzantine princesses.

By the end of the Ilkhanid period in the mid-14th century, the Oghuz tribes that comprised the Aq Qoyunlu confederation roamed the summer pastures in Armenia, in particular, the upper reaches of the Tigris river and winter pastures between the towns of Diyarbakır and Sivas. Since the end of the 14th century, Aq Qoyunlu waged constant wars with another tribal confederation of the Oghuz tribes, the Qara Qoyunlu. The leading Aq Qoyunlu tribe was the Bayandur tribe.

Uzun Hasan used to assert the claim that he was an "honorable descendant of Oghuz Khan and his grandson, Bayandur Khan". In a letter dating to the year 1470, which was sent to Şehzade Bayezid, the then-governor of Amasya, Uzun Hasan wrote that those from the Bayandur and Bayat tribes, as well as other tribes that belonged to the "Oghuz il", and formerly inhabited Mangyshlak, Khwarazm and Turkestan, came and served in his court. He also made the tamga (seal) of the Bayandur tribe the symbol of his state. For this reason, the Bayandur tamga is found in Aq Qoyunlu coins, their official documents, inscriptions and flags.

The Aq Qoyunlu Sultans claimed descent from Bayindir Khan, who was a grandson of Oghuz Khan, the legendary ancestor of Oghuz Turks.

According to Professor G. L. Lewis:

The Ak-koyunlu Sultans claimed descent from Bayindir Khan and it is likely, on the face of it, that the Book of Dede Korkut was composed under their patronage. The snag about this is that in the Ak-koyunlu genealogy Bayindir's father is named as Gok ('Sky') Khan, son of the eponymous Oghuz Khan, whereas in our book he is named as Kam Ghan, a name otherwise unknown. In default of any better explanation, I therefore incline to the belief that the book was composed before Ak-koyunlu rulers had decided who their ancestors were. It was in 1403 that they ceased to be tribal chiefs and became Sultans, so we may assume that their official genealogy was formulated round about that date.