Three cases -- Barefoot v. Estelle, Jones v. United States, and Ake v. Oklahoma -- focus on the role of the expert witness in the criminal trial process, the weight to be given to such testimony, and the constitutional implications of such expert testimony. The cases of Estelle v. Smith, Wainright v. Greenfield, Smith v. Murray, and Illinois v. Allen focus on the privilege against self-incrimination, including the interplay between Miranda rights and mental disability. The case of Ford v. Wainright involves the issue of competence to be executed. Analyses of these decisions show that the members of the Supreme Court share society's uncertainty about mental disabilities and the role of psychiatry in the criminal justice process. Therefore, understanding the current law in such cases depends on understanding the reactions of individual justices and the common and disparate elements within the cases decided on this issue. 947 footnotes.