In Greek mythology, Linus (Ancient Greek: Λῖνος Linos "flax") was a reputed musician and master of eloquent speech. He was regarded as the first leader of lyric song.

Linus's parentage was variously given in ancient sources as: (1) Muse Calliope and Oeagrus or Apollo, (2) Muse Urania and Apollo, (3) Urania and Amphimarus, son of Poseidon, (4) the river-god Ismenius, (5) Urania and Hermes, (6) Muse Terpsichore and Apollo, (7) Muse Clio and Magnes, (8) Pierus, (9) Apollo and Aethusa, daughter of Poseidon, and lastly (10) Apollo and Chalciope. With various genealogy given, Linus was usually represented as the brother of another musician Orpheus. Some accounts instead make the latter his great-grandson through Pierus, father of Oeagrus.

Linus may have been the personification of a dirge or lamentation (threnody), as there was a classical Greek song genre known as linos, a form of dirge, which was sometimes seen as a lament for him. This would account for his being the son of Apollo and a Muse, and by which fact, Linus was also considered the inventor of melody and rhythm or of dirges (thrênoi) and songs in general. Thus, he was called "pantoiês sophiês dedaêkôs" by Hesiod. Either he or his brother Orpheus was regarded as the inventor of the harp; otherwise Linus was credited to be the first to use the harp accompanied with singing. From his father Apollo, he received the three-stringed lute. Later writers wrote verses in his name, some lines of which have survived.

During the Hellenistic period, Alexandrine grammarians even regarded Linus as a historical personage and according to a legend, he was known as the writer of apocryphal works in which he described exploits of the god Dionysus and other mythical legends. With these, he was among other mythical authors, like Musaeus and Orpheus, of Pelasgic writings. Diogenes Laertius ascribes to him several poetical productions, such as a cosmogony on the course of the sun and moon, on the generation of animals and fruits, and the like. His poem begins with the line: "Time was when all things grew up at once;.."

Linus was said to have lived during the reign of Cadmus in Thebes and became important in the art of music along with Amphion and Zethus (1420 BC). In the Suda, Linus was said to have been the first to bring the alphabet from Phoenicia to the Greeks but Diodorus Siculus gives a different account.

...when Cadmus brought from Phoenicia the letters, as they are called, Linus was again the first to transfer them into the Greek language, to give a name to each character, and to fix its shape. Now the letters, as a group, are called "Phoenician" because they were brought to the Greeks from the Phoenicians, but as single letters the Pelasgians were the first to make use of the transferred characters and so they were called.

The same author recounted that Marsyas was flayed by Apollo who broke the strings of the lyre as well as the harmony he had discovered. The harmony of the strings, however, was rediscovered, when the Muses added later the middle string, Linus struck the string with the forefinger, and Orpheus and Thamyras the lowest string and the one next to it. According to Hyginus, Linus won the contest of singing during the games for the Argives conducted by Acastus, son of Pelias.

According to Boeotian tradition, Apollo slew Linus with his arrows for being his rival in a musical contest (Linus's parentage here was described as the son of Urania and Amphimarus) and near Mount Helicon his image stood in a hollow rock, formed in the shape of a grotto. Every year before sacrifices were offered to the Muses, a funeral sacrifice was offered to him, and dirges (linoi) were sung in his honour. His tomb was claimed both by the city of Argos and by Thebes. Chalcis in Euboea likewise boasted of possessing the tomb of Linus, the inscription of which is preserved by Diogenes Laertius.