Year 766 (DCCLXVI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. The denomination 766 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
|Ab urbe condita||1519|
|Balinese saka calendar||687–688|
|Chinese calendar||乙巳年 (Wood Snake)|
3462 or 3402
— to —
丙午年 (Fire Horse)
3463 or 3403
|- Vikram Samvat||822–823|
|- Shaka Samvat||687–688|
|- Kali Yuga||3866–3867|
|Japanese calendar||Tenpyō-jingo 2|
|Minguo calendar||1146 before ROC|
|Seleucid era||1077/1078 AG|
|Thai solar calendar||1308–1309|
892 or 511 or −261
— to —
893 or 512 or −260
- August 25 – Emperor Constantine V publicly humiliates 19 high-ranking officials in the Hippodrome of Constantinople, after discovering a plot against him. He executes the leaders, Constantine Podopagouros and his brother Strategios, and blinds and exiles the rest.
- Autumn – Siege of Kamacha: Abbasid forces under al-Hasan ibn Qahtaba are defeated at the fortress city of Kamacha, in eastern Cappadocia (modern Turkey). A Byzantine relief army (12,000 men) forces the Abbasids to retreat into Armenia.
- Sabin, ruler (khagan) of Bulgaria, flees to the Byzantine fortress city of Mesembria, from where he escapes to Constantinople. Constantine V arranges for the transfer of Sabin's family from Bulgaria.
- Baghdad nears completion as up to 100,000 labourers create a circular city about 1 or 2 km in diameter (depending on the source). In the center of the "Round City" is a palace built for Caliph al-Mansur. The capital is ringed by three lines of walls (approximate date).
- The Karluks defeat the Turgesh Khaganate in Central Asia. Most of Turkestan (former Onoq territory) falls under Karluk rule, except west of Lake Aral, where the loose confederation of the Oghuz Turks is about to emerge.
- March 6 – Chrodegang, Frankish bishop
- August 25
- Abdullah al-Aftah, Shī‘ah Imam and Muslim scholar
- Fallomon mac Con Congalt, king of Mide (Ireland)
- Fujiwara no Matate, Japanese nobleman (b. 715)
- Muhammad ibn al-Ash'ath al-Khuza'i, Muslim governor