In 2002, in Atkins v. Virginia, the United States Supreme Court concluded that the execution of intellectually disabled offenders is cruel and unusual punishment prohibited by the Eighth Amendment. The Court's Atkins ruling not only applied to future capital punishment prosecutions, but also permitted previously death-sentenced state and federal offenders to seek to establish their intellectual disability and resulting ineligibility for execution. Moreover, because of the constitutional nature of the Atkins ruling, state death-sentenced offenders could generally file Atkins claims for collateral relief in both state and federal courts.Since Atkins, almost 600 Atkins claims have been filed in state and federal courts. In 2014, in Hall v. Florida, the Court confirmed the fundamental principles of its Atkins decision and found Florida's implementation of Atkins unconstitutional. This book examines the state and federal legislative and judicial implementation of Atkins prior to Hall and Hall's impact on the future implementation of Atkins. It catalogs the outcomes of Atkins claims filed prior to Hall and describes illustrative successful and unsuccessful Atkins claims. The book also discusses specific Atkins implementation issues that merit future Court consideration in the continuing effort to implement Atkins and exclude intellectually disabled offenders from execution.