The significance of custom in the evolution of legal systems and in the processes of norm‑formation is well established. Within the strategic frameworks of rule‑making, enforceable norms frequently emerge from customary contexts and subsequently attain sophistication through philosophical, theological, and juridical elaboration. The central inquiry animating this study is thus: What is the role and status of custom within the legislative policy and the rule‑making paradigm of Iran? More specifically, does custom possess normative validity in the strategic orientation and procedural mechanisms of the Iranian legal order?

Drawing upon the findings of this research, the authors maintain that, in Iranian law—grounded in Imami jurisprudence—custom lacks autonomous rule‑making authority and cannot serve as an independent source of normative legitimacy for statutes or legal rules. Nevertheless, the derivative or instrumental validity of custom is acknowledged in several domains: the identification of factual subjects, the interpretation of contractual language, the application of statutory provisions to concrete instances, and the supplementation of legislative texts.

Employing a descriptive‑analytical methodology and relying on library‑based data collection, this study systematically explicates and substantiates the foregoing thesis through rigorous scholarly documentation and argumentation.