Ino was the second daughter of Cadmus and Harmonia of Thebes, sister of Semele, Agave, Autonoë, and Polydorus. Together with her sisters she figures among the early nurses of Dionysus. She married the Minyan king Athamas as his second wife and bore him Learchus and Melicertes; she was stepmother to Phrixus and Helle, Athamas's children by the cloud-nymph Nephele.

In the Argonautic back-story, Ino hated Phrixus and Helle and plotted their death by spoiling the seed-corn and bribing an oracle to demand Phrixus's sacrifice. Nephele's flying golden ram rescued the twins; Helle fell into the strait that took her name, while Phrixus reached Colchis with the Golden Fleece.

As nurse of Dionysus, Ino drew Hera's jealousy. In the usual sequel Hera drove Athamas mad; he slew Learchus as if hunting a stag, and Ino fled with Melicertes into the sea. Both were afterwards honoured as marine divinities — Ino as Leucothea, Melicertes as Palaemon. Alternative tellings have Ino herself mad, boiling Melicertes before the leap; Zeus then transforms mother and son out of pity.

Homer's Odyssey knows her as Ino of the fair ankles, once mortal, now Leucothea among the sea-gods, who gives shipwrecked Odysseus her immortal veil. Euripides treated her rivalry with Athamas's later wife Themisto in the lost play Ino; Ovid recounts Hera's punishment of Ino's companions after her disappearance.

The atlas id ino is the Cadmeid princess and Leucothea. Disambiguation pages and modern uses of "Ino" (personal names, acronyms, vessels) are unrelated; do not confuse her with other Leucothea traditions (such as Halia) that some sources merge under the same epithet.