Iacchus

thumb|Iacchus (?), with a torch in each hand, on the Ninnion Tablet, 350s BC, [[National Archaeological Museum of Athens 11036.]]

In ancient Greek religion and mythology, Iacchus (also Iacchos, Iakchos) () was a minor deity, of some cultic importance, particularly at Athens and Eleusis in connection with the Eleusinian Mysteries, but without any significant mythology. He perhaps originated as the personification of the ritual exclamation Iacche! cried out during the Eleusinian procession from Athens to Eleusis. He was often identified with Dionysus, perhaps because of the resemblance of the names Iacchus and Bacchus, another name for Dionysus. By various accounts he was a son of Demeter (or apparently her husband), or a son of Persephone, identical with Dionysus Zagreus, or a son of Dionysus.