The essays examine the development of the present insanity defense, its purpose, and its application, starting with the McNaughton rule of 1843 and continuing through the Hearst and Hinckley trials under the American Law Institute's Model Penal Code formula. The relationships of law and psychiatry and the ethical position of the expert psychiatric witness are also explored. Also covered are the expansion, beginning in the mid-20th century, of the criteria for nonresponsibility for crime and the underlying movement toward liberalism and humanism. The debate over the legal threshold of toleration for harmful behavior inflicted by persons with impaired intellectual and emotional states is also presented in essays focusing on the balancing of the need to defend the structure of society and the moral imperative to protect the psychiatrically disabled. Reference notes and an index are included. Seven of the essays were presented at a 1979 symposium sponsored by the Institute of Social and Behavioral Pathology at the University of Chicago. (Editor summary modified)