Following a brief history of views on insanity and the emergence of Freudian psychology, this book proposes that the definition of criminal responsibility depends on understanding the ties between crime and insanity and that treatment of the criminal is based ultimately on the concept of responsibility. The physical structure of the brain and the effects of injuries to the head are described, as are relationships between mental and physical processes uncovered by scientists. Based on interpretations of Freudian theory, the thought processes of normal minds are explained. A discussion of attempts by criminals and others to pretend to be insane covers hysteria, feigned epileptic fits, and other tactics used by prisoners. Suggestions to correctly diagnose shamming are outlined. An analysis of the abnormal mind emphasizes that when pruned of inessentials the minds of the sane and the insane differ only by degree and that dissociation and conflict are the dominant factors in the phenomenon of insanity. The following agents which some consider to be either the cause or effect of insanity or criminality are explored: epilepsy, heredity, environment, drugs, and alcohol. Other chapters consider cases which hover on the brink of insanity or criminality, suicide, and revolutionaries. Prison punishment methods are severely criticized, and specific reforms are recommended. The concluding survey of criminal responsibility focuses on the McNaughten Rules regarding the insanity plea and then summarizes the trial, appeal, and ultimate reprieve of Ronald True who, although undoubtedly insane, was legally responsible for murdering a woman, but could not be legally executed because he was insane. Future trends in criminology stemming from psychoanalysis and psychological research are predicted. Over 80 references are included.