Generalising the Principle of Complementarity: Framing International Judicial Authority

Abstract

International courts exercise public authority. Their decisions affect individual and collective self-determination. Nowadays, international courts decide on criminal, constitutional and administrative matters, much in the same way as domestic courts. Possible tensions between international and domestic courts raise the question of how to frame international judicial authority vis-à-vis domestic courts in a way that contributes to the legitimacy of their decisions. To respond to these concerns, the article analyses the potential of a generalised principle of complementarity. The principle's underlying idea can be rooted back to several procedural and substantive manifestations of it in human rights courts and in international investment tribunals. It regulates the relationship between international and domestic courts in order to ensure individual legal protection and the balance of individual and collective interests. In accordance with the rationale of the Rome Statute, domestic courts are primary responsible in this regard; and only when they are unable or unwilling may international courts compensate domestic institutional deficiencies, safeguard subjective rights, ensure compliance with international law standards and strengthen domestic capacities. The function of the principle is twofold: (i) to structure the relationship between international and domestic courts—a relationship that is characterised by a division of labour, cooperation and mutual responsibility; and (ii) to normatively guide and evaluate the jurisprudence of international courts. In fulfilling these functions, the legitimating potential of complementarity can best be unfolded.