Ino ( Ινώ, Ἰνὼ ) was a mortal queen in Greek mythology, second wife of Athamas and mother of Learches and Melicertes, daughter of Cadmus and Harmonia and stepmother of Phrixus and Helle.

Alcman called her "Queen of the Sea" (θαλασσομέδουσα), which, if not hyperbole, would make her a doublet of Amphitrite.

Phrixus and Helle, twin children of Athamas and Nephele, were hated by their stepmother, Ino. Ino hatched a devious plot to get rid of the twins, roasting all the towns crop seeds so they would not grow. The local farmers, frightened of famine, asked a nearby oracle for assistance. Ino bribed the men sent to the oracle to lie and tell the others that the oracle required the sacrifice of Phrixus. Athamus reluctantly agreed. Before he was killed though, Phrixus and Helle were rescued by a flying golden ram sent by Nephele, their natural mother. Helle fell off the ram into the Hellespont (which was named after her, meaning Sea of Helle) and drowned, but Phrixus survived all the way to Colchis, where King Aeetes took him in and treated him kindly, giving Phrixus his daughter, Chalciope, in marriage. In gratitude, Phrixus gave the king the golden fleece of the ram, which Aeetes hung in a tree in his kingdom.

Later, Ino raised Dionysus, her nephew, son of her sister Semele, causing Hera's intense jealousy. In vengeance, Hera struck Athamas with insanity. Athamas went mad, and slew one of his sons, Learchus, thinking he was a ram; Ino, to escape the pursuit of her frenzied husband, threw herself into the sea with her son Melicertes. Both were afterwards worshipped as marine divinities, Ino as Leucothea ("the white goddess"), Melicertes as Palaemon. Alternatively, Ino was also stricken with insanity and killed Melicertes by boiling him in a cauldron, then took the cauldron and jumped into the sea with it. A sympathetic Zeus didn't want Ino to die, being grateful for her having raised his son Dionysus, and turned her and Melicertes into Leucothea and Palaemon, respectively.

The story of Ino, Athamus and Melicertes is relevant also in the context of two larger themes. Ino, daughter of Cadmus and Harmonia, had an end just as tragic as her siblings: Semele died while pregnant with Zeus' child, killed by her own pride and lack of trust in her lover; Agave killed her own son, King Pentheus while struck with Dionysian madness and Actaeon, son of Autonoe, the third sibling, was torn apart by his own hunting dogs. Also, the insanity of Ino and Athamus can be explained as a result of their contact with Dionysus, whose presence can cause insanity. None can escape the powers of Dionysus, the god of wine.

When Athamus returned to his second wife, Ino, Themisto (his third wife) sought revenge by dressing her children in white clothing and Ino's in black. Ino switched their clothes without Themisto knowing and she killed her own children.

Odysseus and Ino, Alessandro Allori

Transformed into the goddess Leucothea, Ino also represents one of the many sources of divine aid to Odysseus in the Odyssey (5:333ff), her earliest appearance in literature. Homer calls her "Ino-Leocothea of the beautiful ankles [καλλίσφυρος], daughter of Cadmus, who was once a mortal speaking with the tongue of men, but now in the salt sea-waters has received honor at the hands of the gods". Providing Odysseus with a veil and telling him to discard his cloak and raft, she instructs him how he can entrust himself to the waves and succeed in reaching land and eventually the island of Scheria (Corcyra), home of Phaeaceans.

In historical times, a sisterhood of maenads of Thebes in the service of Dionysus traced their descent in the female line from Ino; we know this because an inscription at Magnesia on the Maeander summoned three maenads from Thebes, from the house of Ino, to direct the new mysteries of Dionysus at Magnesia (Burkert 1992:44).

Moulourian Rock between Athens and Corinth, the place from which Ino jumped into the sea with her son Melikertes, who was saved by a dolphin.

Mercury brings the little Bacchus to the nymph Ino

173 Ino is an asteroid.