Homicidal insanity has remained a vexation to both the psychiatric and legal professions despite the panorama of scientific and social change during the past 200 years. The predominant opinion today among psychiatrists is that no correlation exists between dangerousness and specific mental disorders. But for generation after generation, psychiatrists have reported cases of insane homicide that were clinically similar. Although psychiatric theory changed and psychiatric nosology was inconsistent, the mental phenomena psychiatrists identified in such cases remained the same. The central thesis of Homicidal Insanity is that as psychiatric theory changed, psychiatrists regarded these phenomena variously as symptoms of mental disease or the disease in itself. It is possible to trace these phenomena throughout the history of Anglo-American psychiatric theory and practice. A secondary thesis of the book is that psychiatrists have used these phenomena as predictors and markers in the practical matters of preventing insane homicide and of testifying in the courts to defend the irresponsible and expose the culpable. For 200 years, scientific and philosophical disagreement raised controversy and brought the issues to public attention. Still, to this day no rational method exists to discriminate the dangerous from the harmless in matters of involuntary commitment, nor insanity from crime in the courts.