Workers in the field of delinquency have been familiar since 1925 with the German edition of this book. At that time it was hailed as a masterpiece which would reform methods of dealing with delinquent children. Whereas formerly the superficial explanation given by a child for his conduct was accepted as expressing the true cause of his bad behavior, attitudes changed markedly with the appearance of Aichhorn's book. No longer were superficial explanations considered valid, but investigations were made into the deeper mental structures of the delinquent child with the result that psychoanalytic material came to light which was not only instructive in revealing causes but was often of material aid in correcting the problem. Many of the ideas expressed in this book have been adopted into the literature of child guidance during the decade since the German edition appeared, and technics that were then considered unusual are now commonplace.