The dithyramb (/ˈdɪθɪræm/; Ancient Greek: διθύραμβος, dithyrambos) was an ancient Greek hymn sung and danced in honor of Dionysus, the god of wine and fertility; the term was also used as an epithet of the god. Plato, in The Laws, while discussing various kinds of music mentions "the birth of Dionysos, called, I think, the dithyramb." Plato also remarks in the Republic that dithyrambs are the clearest example of poetry in which the poet is the only speaker.

However, in The Apology Socrates went to the dithyrambic poets with some of their own most elaborate passages, asking their meaning, but got a response of, "Will you believe me?" which "showed me in an instant that not by wisdom do poets write poetry, but by a sort of genius and inspiration; they are like diviners or soothsayers who also say many fine things, but do not understand the meaning of them."

Plutarch contrasted the dithyramb's wild and ecstatic character with the paean. According to Aristotle, the dithyramb was the origin of Athenian tragedy. A wildly enthusiastic speech or piece of writing is still occasionally described as dithyrambic.

Dithyrambs were sung by choirs at Delos, but the literary fragments that have survived are largely Athenian. In Athens, dithyrambs were sung by a Greek chorus of up to fifty men or boys dancing in circular formation, who may or may not have been dressed as Satyrs, probably accompanied by the aulos. They would normally relate some incident in the life of Dionysus or just celebrate wine and fertility.

The ancient Greeks laid out the criteria of the dithyramb as follows:

Competitions between groups, singing and dancing dithyrambs were an important part of the festivals of Dionysus, such as the Dionysia and Lenaia. Each tribe would enter two choirs, one of men and one of boys, each under the leadership of a coryphaeus. The names of the winning teams of dithyrambic contests in Athens were recorded. The successful choregos would receive a statue that would be erected—at his expense—as a public monument to commemorate the victory. However, most of the poets remain unknown.

The earliest mention of dithyramb, found by Sir Arthur Wallace Pickard-Cambridge, is in a fragment of Archilochus, who flourished in the first half of the seventh century BCE: "I know how to lead the fair song of the Lord Dionysus, the dithyramb, when my wits are fused with wine." As a literary composition for chorus, their inspiration is unknown, although it was likely Greek, as Herodotus explicitly speaks of Arion of Lesbos as "the first of men we know to have composed the dithyramb and named it and produced it in Corinth."

The word dithyramb has no known origin, but is frequently assumed not to be derived from Greek. An old hypothesis is that the word is borrowed from Phrygian or Pelasgian, and literally means "Vierschritt", i. e., "four-step", compare iamb and thriambus, but H. S. Versnel rejects this etymology and suggests instead a derivation from a cultic exclamation. Dithyrambs were composed by the poets Simonides and Bacchylides, as well as Pindar (the only one whose works have survived in anything like their original form).