Danny Hill was convicted of torturing, raping, and murdering a twelve-year-old child in Ohio and was sentenced to death. Years later, he sought federal habeas relief, arguing that the state courts had unreasonably rejected his claim that he was intellectually disabled under Atkins v. Virginia. The Sixth Circuit granted relief under the federal habeas statute, relying repeatedly on Moore v. Texas, a decision issued after the relevant state-court adjudications. The Supreme Court vacated that judgment and remanded. The habeas statute permits relief only when the state court decision was contrary to, or an unreasonable application of, Supreme Court law clearly established at the time of the state decision. Atkins prohibited executing intellectually disabled defendants but left states to develop appropriate enforcement standards; later decisions such as Hall and Moore could not simply be treated as already-established law for the earlier adjudication. The Court directed the Sixth Circuit to evaluate Hill’s claim using only the holdings that were clearly established when the Ohio courts ruled.