International Court of Justice (hereinafter I C J) decision on " Dispute Regarding Navigational and Related Rights " ( Costa Rica v. Nicaragua ) has been considered as the first decision of the I C J as the world court. Although being controversial and debatable, in fronting lack of state practice, I C J dynamically invoked the role of individuals in order to identify a rule of special Customary International Law ( hereinafter C I L) as one of the most fundamental and primary sources of public international law enunciated in I C J statute. The decision in question reemphasized the salient role of aule of special C I L in international law and regarded the possible role of individuals on identifying this kind of legal rule. Applying functional approach very dynamically, I C J, as well as possible, has played a considerable role in promoting progressive development of international law.