Actio Popularis before International Courts and Tribunals examines actio popularis in the context of the symbiotic relationship between procedural and substantive normativity in international law. Actio popularis is an important procedural tool devised to address the challenges posed by the relativization of substantive normativity and recognition of norms established to protect collective interests in international law. Farid Ahmadov’s analysis underlines the ineffectiveness of bipolar litigation in enforcement of collective obligations in international law and the importance of introducing new procedural mechanisms to address the challenges posed by the transition from bilateralist to multilateralist normativity. The volume highlights the subtle link between interpretation of standing rules and the ways in which judicial policy concerns inform decisions of international courts and tribunals on admissibility of actio popularis.