Many of our interests have centered about the problems of adolescence. We all know that criminalistic tendencies, those which perhaps control the career of a life time, nearly always first show themselves before the 19th or 20th year. The physiological aspects of this period are the ones that have been most frequently dwelled on, but for our purposes they may be ignored except as they influence the psyche. Overgrowth and restlessness and other phenomena at this time do not directly create criminalism. They have first to effect the mental life which directs action. We have found a fair field for investigation here, and one that opens up whole vistas of possible usefulness. Various new points of departure for legal procedure are to be developed from data gathered concerning this period of life, not the least of which is criticism of that strange arbitrary discrimination under the law which says that boys at 17 and girls at 18 are suddenly responsible, mentally formed, able to properly care for themselves, when a few minutes or days previously they were not. Our studies show that these age limits were not based on practical observations of human beings. Not the least interesting and therapeutically important part of psychological study of offenders is ascertainment of the mental mechanisms and mental content which stand in relation to delinquency. However it may be with older persons, and such experienced men as Parker in New York suggested that with adults this is a rich field for endeavor, we have studied many cases of criminalistic tendency in young people in which the whole trouble centered about some psychically untoward experience or some mental conflict. From this was developed a definite antisocial grudge, or at least an antisocial attitude. These cases, well understood, present some of the most curable criminalistic causes. We must pass with bare mention such data as those on obsessional mental imagery and the formation of mental habits, both of which psychical phenomena play a considerable part in driving towards delinquency. To appreciate what sets the mental machinery turning out antisocial deeds we have to dig deep into many human experiences and many mental activities.