This article concludes that wider implications for penal policy of combining a formal rule that constitutionally guarantees rights of prisoners could only be restricted by primary legislation, with substantive constituted requirements for the objectives of penal legislation and for how these objectives should be met. It is argued that such a rule is potentially applicable not only in Germany but also in other countries with similar constitutional traditions. The article outlines the legislative stalemate that led indirectly to an application being brought. It describes the development of the law relating to the implementation of imprisonment generally since this increased the prospects of success of the application and also predicted the form that the response of the court would take. The article then focuses on the detail of the judgment. Fairly extensive passages of the judgment are quoted in order to convey the reasoning that led to the conclusion that a wide range of issues related to youth imprisonment were of such constitutional significance that the court could direct the legislature in considerable detail on how to deal with them. Next, the article turns to the implications of the judgment for future legislation about the implementation of youth imprisonment in Germany. Particular attention is paid to the importance given to international minimum standards in this regard and to the role research on treatment plays in setting limits to legislative discretion. In both of these respects, the intervention by the court has gone further than ever before. The conclusion considers the wider implications of the German experience for the constitutionalization of penal policy. Notes, references