The practical effectiveness of international treaty and customary law rules depends on their applicability within the domestic legal sphere. The article presents the German constitutional law concepts related to this issue, as they have been authoritatively developed and consolidated by the German Federal Constitutional Court. It demonstrates that the principle of “Völkerrechtsfreundlichkeit” (principle of commitment to international law) cannot, on its own terms, determine the conditions upon which public international law is incorporated into the domestic legal sphere. The same applies to the subsequent question as to the conditions under which international treaty or customary law rules are directly applicable. From a German constitutional law perspective, the question of applicability of norms of public international law within the domestic legal sphere is, rather, a question governed by the principle of “offene Staatlichkeit” (principle of openness of the state towards international law). This is a fundamental principle underlying the German constitution which is also important for the final issue of whether and to what extent so-called ‘treaty override’ is constitutionally permissible.
