In this ground-breaking study, taken on the initiative of US Supreme Court Justice Sandra Day O'Connor, Thomas M Franck, and Gregory H Fox explore the use of international law decisions by national courts. They provide in-depth materials for answers to such critical and practical questions as: to what extent do national judges treat the decision of their international colleagues as binding or persuasive? do national judges regard the outcomes of international decisions as res judicata? as evidence of law or fact? Their analysis and conclusions constitute a valuable assessment of the role of international law in the legal cultures of today’s nations.