Originally published in 1954, this was a new study of aggressive behaviour and phantasies in children of school age, combining the scientific-experimental with the clinical approach. It was, therefore, at the time, likely to be of interest both to experimental psychologists and to clinicians, as well as to all who worked in the fields of child guidance and mental health and were concerned with the welfare of children, including parents and teachers. The author’s group studies of normal, neurotic and delinquent children, made with the help a specially designed pictorial projection test, and the individual studies of her young patients demonstrated objectively the close connection between the forms taken by the aggressive impulse of the child and their relationships with the members of their family. The writer re-defines the concept of aggression, taking a closely argued view that the aggressive urge is a manifestation of the vital impulse to self-realization through exploratory and constructive activities, and that destructive aggression arises only when the ways to constructive activities are blocked at an early age. This theory, with its wide social and educational implications, is put forward as a well-reasoned and hopeful alternative to the traditional view which represents aggressive behaviour as an outcome of an instinct by its very nature asocial and destructive.