The means to ensure compliance with international law differ considerably from those applying in internal law. The latter rely primarily on enforcement by the authority of the state which imposes obedience. Such superior authority does not exist in international relations; international law rather relies on voluntary compliance. But means and methods to ensure such voluntary compliance exist, and over the centuries, they have undergone considerable changes and refinements. As there is a certain strand of opinion denying the character of international law as law because of the (alleged) lack of effective enforcement, a first area of discussion relates to this question, namely whether or why international law, in the light of the compliance problem, is really law. There are classical texts on this issue, which have triggered, and are the basis of, a profound theoretical discussion where the theory of international relations meets with legal theory, including a historical dimension. This leads to an empirical look on circumstances favoring compliance (compliance pulls) of different types: norm internalization, concern for a state’s reputation, sanctions (organized and regulated value deprivation), and withholding certain benefits from a state unless the states complies with certain norms (conditionality). To address the question of compliance only for international law as a whole would be an oversimplification. There are various types of internationally relevant acts to be complied with (standards of compliance) involving particular problems (treaties, customary law, judgments, decisions of international organizations, “soft law”). Various subjects of compliance, i.e., actors or entities whose compliance is at stake, namely states, international organizations, non-state actors, have to be distinguished. All this is the basis for a closer look at means to ensure compliance which have indeed undergone a notable development. Traditional means were, and still are, bilateral in character: bilateral dispute settlement and value deprivation in the relation between a state acting unlawfully and another state trying to make the former state respect the law, traditionally called “reprisal” (or, as the case may be, “retortion”), in the modern terminology “countermeasures.” This traditional tool is still practiced, but it is to a large extent replaced or supplemented by a wide array of other means designed to ensure compliance: individual remedies at the national or international level, international criminal law, special compliance procedures. In connection with all these means, ascertaining facts plays a major role. An important method for this purpose is the so-called reporting system, used in various contexts. In these different procedures, different actors play a role. These are not only the genuine parties to the procedures, but also third parties. Guardians of the public interest, in particular intergovernmental organizations, guide or perform these procedures. The fragmentation of international law has also led to a fragmentation or multiplication of area-specific compliance procedures, i.e., specialized procedures for certain areas of international law, most often for single treaty regimes. These specific procedural set-ups relate inter alia to human rights, arms control and disarmament, the law of armed conflict, environmental law, cultural relations (UNESCO), the law of the sea, and international economic relations.
THE APPEARANCE OF THE PENAL INTERNATIONAL LAW AS A BRANCH OF THE PUBLIC INTERNATIONAL LAW