In 1989, in Penry v. Lynaugh, the U.S. Supreme Court held that the eighth amendment’s cruel and unusual punishment prohibition did not categorically bar the execution of mentally retarded offenders. In 2002, in Atkins v. Virginia, the Supreme Court revisited this issue and held that the execution of mentally retarded offenders is categorically barred by the eighth amendment. These decisions reflect the evolution of capital punishment jurisprudence and the application of this body of law to the case of mentally retarded offenders. This article examines the Court’s treatment of categorical exceptions to the death penalty prior to Penry, its holding in Penry, post-Penry developments leading up tot the Atkins’s decision, the Atkins’s decision, and the implications of the Atkins ruling both for mentally retarded offenders and capital offenders generally. The Atkins ruling may signal that a Court majority now exists for constitutional scrutiny of other substantive and procedural issues concerning capital punishment or at least a return of capital punishment cases to a more prominent role on the Court’s agenda. The Atkins case constitutes a significant benchmark in the continuing evolution of the United States’ constitutional, legislative, judicial, and popular views of capital punishment. References