Secure preventive detention of dangerous offenders has been a major source of debate in German law and practice. Unlike the other two custodial measures of correction and security in the Penal Code (confinement in a psychiatric hospital and in a detoxification clinic), it has served mainly as incapacitation. Judgments by the German Federal Constitutional Court and the European Court of Human Rights challenged this traditional concept of secure preventive detention, which led to a redefinition of the measure. It is now conceived as an offending behavior treatment measure in a secure environment. This article reports on the background of this development and analyzes its implications. Copyright © 2013 John Wiley & Sons, Ltd.