Mount Lykaion (Ancient Greek: Λύκαιον ὄρος, Lýkaion Óros; Latin: Mons Lycaeus) is a mountain in Arcadia, Greece. Lykaion has two peaks: Stefani to the north and St. Ilias (Άγιος Ηλίας, Agios Īlías) to the south where the altar of Zeus is located.

The northern peak is higher, 1,421 m, than the southern, 1,382 m (4,662 and 4,534 ft). Mount Lykaion was sacred to Zeus Lykaios, who was said to have been born and brought up on it, and was the home of Pelasgus and his son Lycaon, who were said to have founded the ritual of Zeus practiced on its summit. This seems to have involved a human sacrifice and a feast in which the man who received the portion of a human victim was changed to a wolf, as Lycaon had been after sacrificing a child. The altar of Zeus consists of a great mound of ashes with a retaining wall. It was said that no shadows fell within the precincts and that any who entered it died within the year. The sanctuary of Zeus played host to athletic games held every four years, the Lykaia.

Archaeological excavations were first carried out in 1897 by K. Kontopoulos for the Greek Archaeological Service, followed by K. Kourouniotes between 1902 and 1909.

The Mt. Lykaion Excavation and Survey Project, a joint effort of the University of Pennsylvania and the University of Arizona began work at the site in 2004, with the aim of continuing the topographical survey begun in 1996 and carrying out a full topographical and architectural analysis not only of the altar and temenos, but of the nearby valley where the Lykaian Games were held. The detailed digital records and drawings of every architectural stone block. To date, a complete map of the area has been made, including not only the Ash Altar and temenos, but also two fountains, including the Hagno fountain mentioned by Pausanias, the hippodrome, the stadium, a building that was probably a bathhouse, the xenon (hotel), a stoa, several rows of seats, and a group of statue bases.

Many of these buildings seem to have been planned in relation to each other: the baths at the northern end of the hippodrome are on the same alignment as it is, and the stoa, the xenon, the lower fountain, and the rows of seats all appear to have been built in an intentionally similar alignment. Just to the north of the stoa four rows of seats were excavated, with the remains of a group of stelae and statue bases nearby. These would have bordered the hippodrome's southern edge, and correspond to an earlier excavated row of seats on the south-eastern edge of the racetrack. The majority of the spectators of events in the hippodrome, however, would have sat on the surrounding hills.

Mt. Lykaion, its religious significance, and its quadrennial athletic games appear with some frequency in the ancient literary sources. The 2nd-century Greek geographer Pausanias provides the greatest amount of information in the eighth book of his Description of Greece, where he discusses Lykaion's mythological, historical, and physical characteristics in detail. More isolated references occur, however, in sources ranging from Plato to Virgil.

Pausanias states that the Arcadians claimed Cretea atop Mt. Lykaion as the birthplace of Zeus, although tradition had handed down at least two other locations for Zeus’ birth.

Lycaon, son of Pelasgus, the mythical founder of the Greek race, is said to have instituted the worship of Zeus at Mt. Lykaion, giving the god the epithet Lykaios and establishing games in his honor. The Bibliotheca, a Roman-era mythological compendium, adds the story that Lycaon attempted to test Zeus’ omniscience by tricking him into eating a sacrifice mixed with human flesh. In punishment, Zeus slew Lycaon and his fifty sons. Other sources, including the Roman poet Ovid, claim instead that Lycaon's punishment was transformation into a wolf, an early example of lycanthropy.