In the year AD
- Muslims under Ibn Hudayj raid Sicily. Meanwhile muslim forces of Caliph Muawiya conquer the state of Fazzan in what is now Libya.
- Tang General Su Dingfang defeats the Western Turks.
- Pope Vitalian issues an edict declaring Latin the exclusive language of all services of the Roman Catholic Church.
- An organ is used to play Church music for the first time in a public service at the Vatican.
- Irish clans the Aradha and the Ui Fidhgeinte fight the Battle of Aine, in which Eoghan, son of Crunnmael, is slain.
- An entry in a Celtic chronicle for the year 666 records a battle between Cruithin and the Ulaid at "Béal Feirsde" ("approach to the sandbank ford"), the earliest reference to the place now known as Belfast.
- Kuryongsa Temple is founded on Korea's Mount Chiaksan by Buddhist saint Uisang.
- Chertsey Abbey, a Benedictine Abbey of St. Peter, is founded at Chertsey by Frithwald, Ealdorman of Surrey.
- Barking Abbey is founded at Barking in Essex by St. Erkenwald, Bishop of London, for his sister St. Ethelburga.
- Exiled French prince Dagobert II marries a Celtic princess, Mathilde of York and moves from Ireland to England.
- Anglo-Saxon nobleman St. Benedict Biscop, founder of Benedictine monasticism in England, becomes a monk during a stay at Lérins, while returning from a pilgrimage to Rome.
- Wu, Empress to Tang ruler Gaozong, orders the deification of Lao Zi, who is given the title "Most High Emperor of Mystic Origin."
- A sixty volume collection of memoirs by Chinese Buddhist pilgrims to India, with forty more volumes of maps and illustrations, is published by Tang Emperor Gaozong, with a preface by the Emperor himself.
These people died in 666:
665 - 666 - 667