In recent years the EU has made extensive use of economic sanctions as a foreign policy tool, to such an extent that it has been said that they have become the default option in diplomatic crises. Measures (known as ‘restrictive measures’ in EU parlance) such as trade embargos, asset freezes and travel bans have been adopted not only to implement United Nations Security Council decisions but also in addition to (as with Iran) or in the absence of (as with Syria and Russia) UN action. At the same time, there has been increasing international condemnation of what critics describe as ‘unilateral coercive measures’, including in a series of UN General Assembly and Human Rights Council resolutions. Taking account of these developments, my research will seek to situate the EU’s use of autonomous sanctions in their international legal context. A two-fold approach will be taken. First, an analysis will be undertaken of how the EU seeks legally to justify its use of economic sanctions. Secondly, the responses of other States to the EU’s actions will be examined. Here, attention will be paid not only to the (possibly self-serving) views of States against whose activities EU sanctions have been directed but also to the reactions of third States, in particular in multilateral fora (regional organisations and the UN).Most legal analysis of the EU’s sanctions has focused on their compatibility with the human rights of their targets in the light, in particular, of a series of decisions by the Luxembourg and Strasbourg courts. My study will not seek to reprise such analyses but, using EU practice as a case study, to examine the extent to which the States and regional organisations are legally entitled to impose autonomous sanctions, having regard to the rights of other States. The project should not only extend our understanding of the status of the EU as an actor in international relations (and as an innovator in methods to secure compliance with international law), and of the vexed relationship between EU law international law, but also provide more general insights into the legal consequences of State responsibility in the areas of human rights, the non-proliferation of weapons of mass destruction and environmental protection, and the conditions for the legality of countermeasures in contemporary international law.