Many governments accept in principle the existence of customary international law, although there are differing opinions as to what rules are contained in it.
[7] The United Nations General Assembly welcomed the Conclusions and encouraged their widest possible dissemination.
Instead, Article 1(2) of Additional Protocol I dictates that customary international law governs legal matters concerning armed conflict not covered by other agreements.
"[21] A marker of customary international law is consensus among states exhibited both by widespread conduct and a discernible sense of obligation.
[22] In relation to the psychological element that is opinio juris, the International Court of Justice further held in North Sea Continental Shelf that "not only must the acts concerned amount to 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 of law requiring it ...
"[23] The Court emphasised the need to prove a "sense of legal duty" as distinct from "acts motivated by considerations of courtesy, convenience or tradition".
The existence of bilateral customary law was recognized by the International Court of Justice in the Right of Passage Over Indian Territory case between Portugal and India, in which the court found "no reason why long continued practice between the two states accepted by them as regulating their relations should not form the basis of mutual rights and obligations between the two states".
[25] Other examples accepted or claimed as customary international law include immunity of visiting foreign heads of state and the principle of non-refoulement.
In 1993, the United Nations Security Council adopted the Geneva Conventions as customary international law.