• Protocol to Prevent, Suppress and Punish Trafficking in Persons, Especially Women and Children, supplementing the United Nations Convention against Transnational Organized Crime; • Protocol against the Smuggling of Migrants by Land, Sea and Air, Supplementing the United Nations Convention against Transnational Organized Crime; • United Nations Convention against Corruption. 2.3. CUSTOMARY INTERNATIONAL LAW RELEVANT TO TRAFFICKING International customary law is defined as “evidence of a general practice accepted as law”.6 Customary international law does not need to be written. A rule will be considered to be customary if: (i) it reflects general and uniform State practice; and (ii) such practice is accompanied by a subjective sense of legal obligation (opinio juris).7 It is not necessary that all countries recognize a rule of customary international law for the norm to exist and to bind them. All that is required is a general consensus that the rule in question is in fact an obligation and a sufficient level of conforming State practice.8 In principle, custom and treaty law are equal in value. If there is a conflict between a customary and a treaty-based rule then the one 6 In the context of trafficking, customary international law is important for several reasons. First, not all States have become parties to all relevant instruments. The characterization of a rule as part of customary international law elevates that rule (and any resulting obligation) to one of universal applicability. For example, the prohibitions on torture and discrimination are widely considered to be norms of customary international law operating to constrain all States, not just those that are party to the relevant international and regional conventions. The conclusions of the Commentary on how such prohibitions relate to trafficking would therefore apply to all States. Another example is provided by the customary rules relating to the formation and interpretation of treaties. These rules operate to bind all States, not just those that are party to the Vienna Convention on the Law of Treaties. In this area as in all others, customary international law can also play an important role in shedding light on the actual content of codified rules. For example, it has been frequently argued that the international prohibition on slavery, as codified in various human rights treaties, has been expanded (by opinio juris as well as by State practice) to include contemporary manifestations of slavery, such as trafficking. Such a conclusion, if proved, Statute of the International Court of Justice, Article 38 (1)(b). “Not only must the acts concerned be a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule requiring it. … The States concerned must feel that they are conforming to what amounts to a legal obligation.” (North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands) (1969) ICJ Reports 3, 44. See also Ian Brownlie, Principles of Public International Law, 4th ed. 1990, pp. 5-7. 7 In the Nicaragua Case, the International Court of Justice held that: “In order to deduce the existence of customary rules, the Court deems it sufficient that the conduct of States 8 that emerged later in time or is intended as a specialized rule will generally prevail. should in general be consistent with such a rule; and that instances of State conduct inconsistent with a given rule should generally have been treated as breaches of that rule, not as indications of the recognition of a new rule.” Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States) (1986) ICJ Reports pp. 3, 98. Note also the well-established rule that States objecting to a norm of international customary law when it is being formed are not bound by it (the rule of the “persistent objector”). “[I]n . principle, a State that indicates its dissent from a practice while the law is still in the process of development is not bound by that rule even after it matures”: American Law Institute, Restatement (Third) of the Foreign Relations Law of the United States (1990), p. 102. COMMENTARY 23