Chapter 26 describes the cases that have defined the evolution of the United States’ relationship with the death penalty. Over time, the country has gradually narrowed the pool of those eligible to be executed, prohibiting the infliction of death on individuals the mental retardation, mental illness, and most, recently, adolescents. These cases are important for forensic professionals who may be involved in the evaluation or treatment of capital defendants. The cases in this chapter are Estelle v. Smith, Ake v. Oklahoma, Ford v. Wainwright, Payne v. Tennessee, State v. Perry, Atkins v. Virginia, Roper v. Simmons and Panetti v. Quarterman. The new cases further refine issues related to intellectual disability standards and procedural protections. These include Ryan v. Gonzales, Hall v. Florida, Moore v. Texas and Mcwilliams v. Dunn.