The European Union’s economic sanctions against Iran and Syria have been both wide-ranging in scope and far-reaching in impacting the lives of ordinary people. It is noteworthy that the bulk of the EU’s sanctions have been adopted without the authority and support of the UNSC—an organ in whose hands the coercive activities are centralized and monopolized according to Chapter VIII of the UN Charter. This chapter describes sanctions regimes introduced by the EU, and then moves to analyze the basis on which they have been adopted. The law applicable to sanctions raises constitutional issues of the relationship between the UN and EU and of the rights and obligations of States under constituent instruments of both organizations. It draws on various options of the relationship between UN and EU focused upon in international judicial practice, and the ways in which EU’s claims to ‘autonomy’ from the UN should be properly handled. As a next step, the legality of the EU’s measures under general international law is examined. It then assesses the propriety of sanctions in the light of broader policy and institutional considerations.