The characteristic of cynocephaly, or cynocephalus (/saɪnoʊˈsɛfəli/), having the head of a canid, typically that of a dog or jackal, is a widely attested mythical phenomenon existing in many different forms and contexts. The literal meaning of cynocephaly is "dog-headedness"; however, that this refers to a human body with a dog head is implied. Such cynocephalics are known in mythology and legend from many parts of the world, including ancient Egypt, Libya, Greece, India and China. Further mentions come from the medieval East and Europe. In modern popular culture cynocephalics are also encountered as characters in books, comics, and graphic novels. Cynocephaly is generally distinguished from lycanthropy (werewolfism) and dogs that can talk.

In addition, the Greeks and Romans called a species of apes cynocephalus (these apes are suspected to be baboons).

The word cynocephaly is taken (through Latin) from the Greek word κυνοκέφαλοι kynokephaloi, plural of the word κυνοκέφαλος, from kyno– (combining form of κύων kyōn) meaning "dog" and κεφαλή kephalē meaning "head".

The same "dog" root is found in the name Cynomorpha ("dog-shaped") for a sub-group of the family of Old World monkeys, which contains many species of macaques and baboons.

Cynocephaly was familiar to the ancient Greeks from representations of the Egyptian gods Duamutef (son of Horus), Wepwawet (the opener of the ways), and Anubis (the god of the dead) with the heads of jackals. The Greek word (Greek: κῠνοκέφᾰλοι) "dog-head" also identified a sacred Egyptian baboon with a dog-like face. Rather than literally depicting a hybrid human-animal state, these cynocephalic portrayals of deities conveyed those deities' therianthropic ability to shift between fully human and fully animal states. In an Ancient Egyptian hybrid image, the head represents the original form of the being depicted, so that, as the Egyptologist Henry Fischer put it, "a lion-headed goddess is a lion-goddess in human form, while a royal sphinx, conversely, is a man who has assumed the form of a lion." This non-literal approach to depicting deities may have confused visitors from Greece, leading them to believe that Egyptians worshipped cynocephalic gods, or even that mortal cynocephalic entities populated Egypt.

Reports of dog-headed races can also be traced back to Greek antiquity. In the fifth century BC, the Greek physician Ctesias, in his Indica, wrote a detailed report on the existence of cynocephali in India. Similarly, the Greek traveler Megasthenes claimed to know about dog-headed people in India who lived in the mountains, communicated through barking, wore the skins of wild animals and lived by hunting. Claudius Aelianus also mentioned the dog-headed tribes in India, and he, too, wrote that they are of human shape and clothed in the skins of beasts. He also added that although they have no speech and howled to communicate, they were capable of understanding the Indian language. Herodotus reports claims by ancient Libyans that such creatures inhabit the east of their lands, as well as headless men and various other anomalies.

The best estimate for the place where the battle between the Argonauts and the Cynocephali took place is modern day North Serbia or South Hungary.

Some Greek writers also mention the Hemicynes (singular, Hemicyon), meaning half-dogs (from "ἡμι" meaning "half" and "κύων" meaning "dog").