This monograph is the third edition of a well known work which first appeared in 1923 as a section of Aschaffenburg's Handbuch der Psychia-trie. It has been carefully revised and enlarged. In the general part the constitution of the psychopath has been treated anew from the standpoint of psychophysical unity, and normal, abnormal and psychopathic are brought to a common ground for discussion. The theories of constitution and localization, proposed by Gruhle, Koch, Tramer, Homburger, Kahn, J. H. Schultz, Kretschmer and Ewald, are explained and evaluated. Kahn's ideas seem to be the most impressive. The material formerly in a section called “Psychopathic Personality and Legal Proceedings” may now be found under the title “Psychopathic Personality and Psychoses” at the end of the general part, where it has been greatly enlarged and contains the new developments.