According to one account the daughter of Ares and Aphrodite, and wife of Cadmus. With Cadmus, she was the mother of Ino, Polydorus, Autonoe, Agave and Semele
When the government of Thebes was bestowed upon Cadmus by Athena, Zeus gave him Harmonia to wife. All the gods honoured the wedding with their presence. Cadmus (or one of the gods) presented the bride with a robe and necklace, the work of Hephaestus. This necklace brought misfortune to all who possessed it. With it Polynices bribed Eriphyle to persuade her husband Amphiaraus to undertake the expedition against Thebes. This led to the death of Eriphyle, of Alcmaeon, of Phegeus and his sons.
Even after the necklace had been deposited in the temple of Athena Pronoia at Delphi, its baleful influence continued. Phayllus, one of the Phocian leaders in the Sacred War (352 B.C.) carried it off and gave it to his mistress. After she had worn it for a time, her son was seized with madness and set fire to the house, and she perished in the flames.
According to another account, Harmonia was from to Samothrace and was the daughter of Zeus and Electra, her brother Iasion being the founder of the mystic rites celebrated on the island.
Finally, Harmonia is rationalized as closely allied to Aphrodite Pandemos, the love that unites all people, the personification of order and civic unity, corresponding to the Roman Concordia.
Edited and wikified from a 1911 encyclopedia