Phaenias of Eresus (Ancient Greek: Φαινίας ὁ Ἐρέσιος, Phainias; also Phanias (Φανίας)) was a Greek philosopher from Lesbos, important as an immediate follower of and commentator on Aristotle. He came to Athens about 332 BCE, and joined his compatriot, Theophrastus, in the Peripatetic school. His writings on logic and science appear to have been commentaries or supplements to the works of Aristotle and Theophrastus. He also wrote extensively on history. His works have only survived in fragments quoted by other authors.