among states as exhibited both by widespread conduct and a discernible sense of obligation. As such, it is not necessary for a country to sign a treaty for customary international law to apply and it therefore applies in all OSCE participating States. Customary international law cannot be declared by a majority of states for their own purposes; it can be discerned only through actual widespread practice. For example, laws of war were long a matter of customary law before they were codified in the Geneva Conventions and other treaties. A particular category of customary international law, ius cogens, refers to a principle of international law so fundamental that no state may opt out by way of treaty or otherwise. The prohibitions of torture, slavery, genocide, racial discrimination and crimes against humanity are widely recognized as peremptory norms, as reflected in the International Law Commission’s articles on state responsibility.120 Customary international law is an important source of law. It is particularly relevant as it relates to human rights law as well as counter-terrorism. It is generally held that there are two essential elements to customary international law: general practice and opinio iuris. A custom may be said to exist only where there is a certain degree of concurrency of behaviour amongst the relevant actors. This is just as true for international custom as it is for local custom. According to the International Court of Justice, for a rule to become part of customary international law, evidence must be shown of a “constant and uniform usage practiced by States.”121 State practice, in this respect, may include treaties, decisions of national and international courts, national legislation, diplomatic correspondence, opinions of national legal advisors and the practice of international organizations. In some cases, a treaty provision might be regarded as becoming part of customary international law “even without the passage of any considerable period of time” if the treaty enjoyed a “very widespread and representative participation.”122 Concurrency of practice is clearly not sufficient, in and of itself, for a practice to be regarded as legally or morally obligatory (consider, e.g., the practice of “rolling out the red carpet” for foreign dignitaries). In addition, there must be evidence of the states concerned regarding themselves as being legally obliged to act in that manner. Opinio iuris, therefore, is the “subjective” or “mental” element of custom, and one that is critical for a concurrent practice to be regarded as legally binding. In addition to these two elements, a third factor is frequently stressed: that the principle in question be of a “fundamentally norm-creating character”123 such as to stipulate, in relatively clear terms, what is required of states. Some rights, such as the right to development, may well fail on this particular test. It is not infrequently the case that certain rights are spoken of, not only in terms of their being part of customary international law, but as having the status of ius cogens. The term ius cogens 120 International Law Commission, Draft Articles on responsibility of states for internationally wrongful acts with commentaries, adopted 2001, (UN, 2005), p. 281 (footnote 675); see also International Criminal Tribunal for the former Yugoslavia, Prosecutor v. Furundzija, Case IT-95-17/1, judgment of 10 December 1998. 121 ICJ, Asylum (Colombia v. Peru), 1950 I.C.J. Reports 266, para. 276-77. 122 ICJ, North Sea Continental Shelf (F.R.G./Denmark; F.R.G./Netherlands), 1969 ICJ Reports 3, paras. 73-74. 123 Ibid., para. 72. 56 Countering Terrorism, Protecting Human Rights