Anselm of Canterbury’s Cur Deus Homo (‘Why Did God Become Human?’, 1098 AD) is the most influential atonement treatise in Western Christian history. Anselm’s argument: sin is an infinite offense against God’s honor (the feudal framework — dishonoring one’s overlord requires proportionate satisfaction). Humanity owes a debt it cannot pay — only God can pay it, but only humanity owes it. Therefore only a God-man can satisfy the debt. Christ’s death, as the one sinless human being, offers to God a gift of infinite worth that more than compensates for humanity’s infinite debt. Satisfaction theory shifts the center of atonement thinking from cosmic battle (Christus Victor) to legal/commercial transaction. It dominates Western Catholic theology until and beyond the Reformation. Anselm’s framework is reworked by the Reformers — especially Calvin — into Penal Substitution, which makes the satisfaction not about honor but about legal penalty.