The principles for juvenile protection established after the Second World War place special juvenile judges in charge of determining protection and education measures for juveniles. Measures are to be determined on an individual basis using information gathered in a background check. Judges may intervene at any point to modify educational measures for assuring continuity of treatment. The juvenile judge thus becomes an authentic agent of prevention with the goals of education and protection. The inspiration for putting these principles into practice has derived largely from the New Social Defense Movement, which seeks to bring about realistic and humane changes in the classical justice system. Support for these directions of juvenile justice has been voiced at a number of conferences since 1958, especially by Marc Ancel. In 1970, under the influence of the movement, legislators changed the civil code to permit intervention of juvenile justices in cases of adolescents at risk and in need of educative assistance. Critics argue that sociocultural changes in environment are more important than reeducation of juvenile delinquents and that juvenile judges do little more than stigmatize minors by exercising authoritarian social control. Other critics believe that only the offense should be considered in judges' decisions, not the personality of the offender. There may be some truth in the criticisms if the treatment of juveniles is reduced to educative actions and automatic conditioning without regard for the individual personality. For the greatest effectiveness, juvenile judges must never lose sight of the responsibilities associated with the powers to exercise parental control and to limit individual liberties. In making decisions, judges must pay special attention to the results of medico-psychological and social investigations, but the information must remain otherwise privileged. In certain countries, social administrative agencies have assumed partial responsibility for juvenile rehabilitation decisions but in France and most other European countries the principal juvenile protection decisions are traditionally in the judicial specialists' area of competence. In keeping with the ideas of the New Social Defense Movement, juvenile judges intervene when certain juveniles disturb the public order, are totally resistant to parental authority, are in danger as a result of extrafamilial circumstances, or are abused or neglected by their parents. Notes are supplied.