This paper is one of the most notable contributions of recent years to the anthropological and psychological study of the juvenile criminal. It is based on careful observation of a series of twenty-two youthful assassins who were under the author's care for considerable periods of time in the Plötzensee Prison at Berlin. Full notes are given of each case, comprising a history of the crime, the personal and family antecedents of the criminal, his physical and mental condition, with anthropometric details, and, in most of the observations, with good photographs of the individual at different ages. The main facts brought out by the inquiry are then summarised, and their bearing on various problems of criminology is discussed with that union of thoroughness of method and breadth of view which invariably distinguishes Dr. Baer's work A paper of this scope and character cannot, of course, be adequately treated within the limits of a short notice, and the present résumé does not aim at more than indicating a few of its salient points.