The Theogony is structured as a genealogy, and the genealogy is the argument. It opens with the poet meeting the Muses on Mount Helikon, who give him a staff and the authority to sing, and who remark pointedly that they can tell truths or convincing falsehoods as they choose. Then the sequence begins: Chaos first, then Gaia, earth, then Tartaros and Eros. Gaia produces Ouranos, sky, and lies with him, and their children include the twelve Titans, the Cyclopes and the hundred-handed giants.
Ouranos prevents his offspring from emerging. Gaia makes a sickle of adamant, and her youngest son Kronos castrates his father; from the blood come the Furies and the Giants, and from the severed genitals thrown into the sea comes Aphrodite. Kronos, warned that he will be overthrown in turn, swallows each child at birth until his wife Rhea substitutes a stone for Zeus and hides the infant in Crete. Grown, Zeus forces the disgorging of his siblings and leads them against the Titans in the ten-year Titanomachy, freeing the hundred-handed ones to break the deadlock and confining the defeated in Tartaros. A final challenge from the monster Typhoeus is put down, and the gods invite Zeus to rule.
The poem then catalogues Zeus's marriages, beginning with Metis, whom he swallows so that no son of hers can repeat the pattern. That closes the loop. The succession of violence stops because Zeus alone has learned how it works.
Between the major episodes the Theogony works through long lists of names: the rivers and the daughters of Ocean, the offspring of Night, which include Doom, Blame, Grief and the Fates, the children of the sea deities. These catalogues are not filler. They organise the world by descent, so that abstractions, rivers, monsters and Olympians all occupy positions in one family. A separate passage praises Hekate at length, out of proportion to her role elsewhere, which has led some to suspect an interpolation and others to argue for a local Boiotian attachment.