The Theogony (Ancient Greek: Θεογονία, romanized: Theogonía, lit. 'the genealogy or birth of the gods') is a poem by Hesiod (8th–7th century BC) describing the origins and genealogies of the Greek gods, composed c. 730–700 BC. It is written in the epic dialect of Ancient Greek and contains 1,022 lines. It is one of the most important sources for the understanding of early Greek cosmology.

Hesiod's Theogony is a large-scale synthesis of a vast variety of local Greek traditions concerning the gods, organized as a narrative that tells how they came to be and how they established permanent control over the cosmos. It is the first known Greek mythical cosmogony. The initial state of the universe is chaos, a dark indefinite void considered a divine primordial condition from which everything else appeared. Theogonies are a part of Greek mythology which embodies the desire to articulate reality as a whole; this universalizing impulse was fundamental for the first later projects of speculative theorizing.

Further, in the "Kings and Singers" passage (80–103) Hesiod appropriates to himself the authority usually reserved to sacred kingship. The poet declares that it is he, where we might have expected some king instead, upon whom the Muses have bestowed the two gifts of a scepter and an authoritative voice (Hesiod, Theogony 30–3), which are the visible signs of kingship. It is not that this gesture is meant to make Hesiod a king. Rather, the point is that the authority of kingship now belongs to the poetic voice, the voice that is declaiming the Theogony.

Although it is often used as a sourcebook for Greek mythology, the Theogony is both more and less than that. In formal terms it is a hymn invoking Zeus and the Muses: parallel passages between it and the much shorter Homeric Hymn to the Muses make it clear that the Theogony developed out of a tradition of hymnic preludes with which an ancient Greek rhapsode would begin his performance at poetic competitions. It is necessary to see the Theogony not as the definitive source of Greek mythology, but rather as a snapshot of a dynamic tradition that happened to crystallize when Hesiod formulated the myths he knew—and to remember that the traditions have continued evolving since that time.

The written form of the Theogony was established in the 6th century BC. Even some conservative editors have concluded that the Typhon episode (820–68) is an interpolation.

Hesiod was probably influenced by some Near-Eastern traditions, such as the Babylonian Dynasty of Dunnum, which were mixed with local traditions, but they are more likely to be lingering traces from the Mycenaean tradition than the result of oriental contacts in Hesiod's own time.

The decipherment of Hittite mythical texts, notably the Kingship in Heaven text first presented in 1946, with its castration mytheme, offers in the figure of Kumarbi an Anatolian parallel to Hesiod's Uranus–Cronus conflict.

One of the principal components of the Theogony is the presentation of what is called the "succession myth", which tells how Cronus overthrew Uranus, and how in turn Zeus overthrew Cronus and his fellow Titans, and how Zeus was eventually established as the final and permanent ruler of the cosmos.