The historical development of Anglo-American insanity perspectives is reviewed, and psychology and psychiatry's growing involvement with law is investigated. The trend of courts toward psychological dimensions of the insanity defense and toward treatment versus punishment is discussed. Basic mental health issues posed by the insanity defense are investigated, and it is contended that psychological experts alone cannot solve ambiguities in the insanity defense. The treatment and rehabilitation of the insane are explored, along with when and why punishment should be used in conjunction with the insanity defense. Insanity is viewed from three different perspectives: that of the lay person (juror); that of the neuropsychologist; and that of the defendant turned patient. A case study is used to examine the neuropsychological perspective because current advances in neuropsychology threaten to negate some of the commonly held assumptions about personhood, responsibility, and insanity. An effort is made to show why the insanity defense is different from other excusing conditions and why shifting the burden of proof to the defense is conceptually sound. In proposing a new test for insanity, the author defends the thesis that the long-standing actus reus-mens rea division contributes to problems and loopholes in the insanity defense. He proposes a revision of Fingarette and Hasse's "disability of mind" doctrine. 528 references, 4 tables.