In theory, judicial decisions do not constitute a formal source of law; in practice, however, they play a substantial role in the development of international law.

When the State practice is either ambiguous, non-existent, sparse, or contradictory, courts get involved in determining the rules of law in order to decide a legal issue and in this process they create new rules. Decisions rendered by the courts are of immense value; and in those cases where there is no preexisting rule, these decisions become a direct source of law.