Phaethon (; Ancient Greek: Φαέθων, romanized: Phaéthōn, lit. 'shiner', pronounced [pʰa.é.tʰɔːn]), also spelled Phaëthon, is the son of the Oceanid Clymene and the sun god Helios in Greek mythology.

According to most authors, Phaethon is the son of Helios who, out of a desire to have his parentage confirmed, travels to the sun god's palace in the east. He is recognised by his father and asks for the privilege of driving his chariot for a single day. Despite Helios' fervent warnings and attempts to dissuade him, counting the numerous dangers he would face in his celestial journey and reminding Phaethon that only he can control the horses, the boy is not dissuaded and does not change his mind. He is then allowed to take the chariot's reins; his ride is disastrous, as he cannot keep a firm grip on the horses. As a result, he drives the chariot too close to the Earth, burning it, and too far from it, freezing it.

In the end, after many complaints, from the stars in the sky to the Earth itself, Zeus strikes Phaethon with one of his lightning bolts, killing him instantly. His dead body falls into the river Eridanus, and his sisters, the Heliades, cry tears of amber and are turned to black poplar as they mourn him.

Phaethon's tale was commonly used to explain why uninhabitable lands on both sides of extremity (such as hot deserts and frozen wastelands) exist, and why certain peoples have darker complexions, while his sisters' amber tears accounted for the river's rich deposits of amber.