Rabbinic tradition traces the genealogy of the Messiah, on the one side, to a father having intercourse with one of his daughters, and, on the other, to a father-in-law having intercourse with his daughter-in-law. (Also Moses, the lawgiver, was the product of a union between a nephew and an aunt.) The essay considers the significance of these extraordinary genealogies. It concludes that in rabbinic tradition the precondition for both the arrival of the Messiah and the creation of law is erotic attachment.