Yvain, Chrétien's masterpiece, has been conventionally seen as a counterpoise to Erec et Enide, attempting to reconcile the conflicting claims of love and chivalry. The several versions of this interpretation are misleading, if not quite wrong, because they divert our attention from what is special about Yvain to what it has in common with Erec. In all of them the lion is peripheral, although for Chrétien himself the lion gave the romance its name: Le Chevalier au lion. I intend to argue that Yvain is rather a critique of the Arthurian ideal, using patristic — or, if one prefers, Christian — psychology to show its hero fall victim to the sins of superbia, invidia, and ira in the first part and triumph over them in the second. Chrétien, I propose, made the lion a symbol of ira as a power of the soul and as ambivalent emotion, so that the two-part figure of the Chevalier au Lion — Yvain with his lion — dramatizes the restoration of ideal order within Yvain himself. Since the story of Yvain derives almost certainly from a Celtic source, Chrétien's originality consists not in the main events but in their disposition and in the emphasis assigned them in order to reveal their psychological and moral significance. I shall use comparisons with the Welsh story of Owein and the Lady of the Fountain to set that originality in relief, for whether the Welsh romance itself is the ultimate source of Yvain or both develop from some common source, it very likely approximates the form of the story prior to Chrétien's revision. It contains all the essential elements of Chrétien's romance — except Yvain's meeting with the hermit and the dispute between the daughters of the Lord of Noire Espine — masterly in detail but loosely connected, without moral focus or thematic coherence. Yvain, on the other hand, is distinguished, as this essay will try to show, by Chrétien's use of a progression of parallel incidents, together with the symbolic figure of the lion, to reveal gradually the meaning of the whole.