This book describes and analyzes the impulses of the writer, pediatrician, and educator Janusz Korczak (1878-1942) for childhood research. As an established practitioner and (until now underestimated) theorist, Korczak tested and further developed many research methods for interacting with children and understanding the child: the observation and description of the child, the self-observation of the adult, experiments and statistical studies on the child's social behavior, the benefits of written communication, as well as conversations and writing with children.