quality:correction
Recognition

The International Court of Justice Statute defines customary international law in Article 38(1)(b) as "a general practice accepted as law". This is generally determined through two factors: the general practice of states, and what states have accepted as law (opinio juris sive necessitatis). This means that many states need to engage in the practice (in particular, great powers) and that states engage in the practice out of a sense of legal obligation (rather than custom or habit).