Yvain, the Knight of the Lion (French: Yvain ou le Chevalier au Lion) is an Arthurian romance by French poet Chrétien de Troyes. It was written c. 1180 simultaneously with Lancelot, the Knight of the Cart, and includes several references to the narrative of that poem. It is a story of knight-errantry, in which the protagonist Yvain (Ywain) is first rejected by his lady for breaking a promise, and subsequently performs a number of heroic deeds in order to regain her favor. The poem has been adapted into several other medieval works, including Iwein and Owain, or the Lady of the Fountain.
