As international lawyers know, the concept of lies at the heart of fundamental debates on the nature and function of international law. Sanctions are of course linked to the general problem of compliance inherent in the prescriptive nature of any legal order. Under general international law, there was and still is no socially organized sanction along the lines of states' legal systems. Reactions to violations of the horizontal system that is international law have traditionally been unilateral, i.e., have taken the form of private justice. States enforced their own rights and, in invoking responsibility, freely determined the legal consequences they ascribed to other states' infringement of their rights, having recourse to coercive measures if necessary. In short, unpredictable decentralized reactions to violations of international law were and still are, to a large extent, the rule in international society.However, the progressive institutionalization of international society has had an impact not only on the structure and normative content of international law, but also on its enforcement. On the one hand, there has been a progressive limitation of resort to unilateral measures, not only through the regulation of the traditional sovereign right to use military force - from the outlawry of war to the outlawry of military reprisals - but equally with efforts to constrain non-military countermeasures such as unilateral trade measures, whether through the establishment of prior conditions or through subsequent control - under the law of international economic institutions (World Trade Organization, European Union), the law on state responsibility, or charter law.On the other hand, beginning with the United Nations charter, we have seen the growth of collective institutionalized responses to breaches of international law. This has gone hand in hand with the creation and expansion of a domain of public interest or international public policy, the emergence of the legal notion (and legal fiction) of an international community, and the hierarchization of rules due to a growing value-oriented international law, i.e., the creation of a core of norms deemed fundamental in the sense that they are directed to the protection of certain overriding community values, or indispensable for the functioning of a highly complex and interdependent international society, and the nonobservance of which would affect the very essence of the international legal system. These norms may be assigned different purposes: to maintain some semblance of an international public order based on the need for stability; to ensure peaceful transformation of that order based on notions of justice; to preserve a certain universal moral foundation based on a minimum core of humanitarian or ethical norms; or, more basically, to ensure the physical protection or very survival of mankind. Hence they are wide-ranging and encompass the non-use of force, selfdetermination, basic principles of human rights and humanitarian law, and, perhaps, include the emerging norms relating to the global commons or the protection of the natural environment.The term sanctions as a term of art in international law is now principally reserved for centralized mechanisms within the aegis of international organizations, going beyond the usual mechanisms found in certain constituent instruments of international organizations, such as expulsion or suspension of membership rights. Sanctions are now said to be:reactive measures applied by virtue of a decision taken by an international organization following a breach of an international obligation having serious consequences for the international community as a whole, and in particular... certain measures which the United Nations is empowered to adopt, under the system established by the Charter, with a view to the maintenance of international peace and security.1Such collective measures are a logical response to the need to protect community values and interests. …