In This Article Expand or collapse the "in this article" section Complementarity Principle

  • Introduction
  • General Overviews
  • Commentaries
  • Origins and Drafting History
  • Elements and Other Statute Provisions
  • Sovereignty
  • Trigger Mechanisms
  • Fair Trial Considerations
  • Prosecutorial Discretion
  • Amnesties and Alternative Forms of Justice
  • Universal Jurisdiction
  • Relationship with Other Institutions
  • Nonstate Parties

International Law Complementarity Principle
Olympia Bekou
  • LAST REVIEWED: 25 June 2013
  • LAST MODIFIED: 25 June 2013
  • DOI: 10.1093/obo/9780199796953-0071


Complementarity is a fundamental principle upon which the International Criminal Court (ICC) is premised. As such, it has been subjected to much academic scrutiny, both in terms of its constituting elements and the potential ramifications of its use. Complementarity governs the relationship between the ICC and national legal orders. Article 17 of the Rome Statute allows the ICC to step in and exercise jurisdiction where states are unable or unwilling genuinely to investigate or prosecute, without replacing judicial systems that function properly. “Unwillingness” and “inability” are key concepts in the determination of the admissibility of a case before the ICC. A state may be determined to be “unwilling” when it is clearly shielding someone from his or her responsibility for ICC crimes. A state may be “unable” when its legal system has collapsed. The statute provides some guidance in the determination of these elements but the precise thresholds are subject to much academic debate as well as judicial determination in the emerging case law of the ICC. Moreover, issues relating to fairness, amnesties, pardons, or other nonjudicial mechanisms and their role in the determination of the admissibility of a case before the ICC have also been controversial and merit further exploration, not least because the statute remains silent on how they fit with complementarity. The incentive of avoiding the ICC’s jurisdiction, described also as complementarity’s “catalytic effect,” may not encourage states to investigate and prosecute if the benefits of overseeing national prosecutions are outweighed or negated by the difficulties of engaging in the process of criminal justice for atrocities and the relative incapacity of national institutions. Where inability or unwillingness to investigate or prosecute is encountered, it may be necessary to shift the balance of advantages and disadvantages for and against prosecution in order to facilitate states to fulfill their role under the ICC’s complementarity regime. Over the years, a more positive approach to complementarity has been put forward and the meaning of complementarity as this was foreseen originally has begun to change. Following the Kampala Review Conference, positive complementarity increased in significance, and capacity building has firmly entered the vocabulary of international criminal lawyers. The ability of states to fulfill this role has significance not only for their sovereign equality in the community of states, but also for the effectiveness of the ICC at fighting impunity and delivering justice that is meaningful for victims of mass atrocity.

General Overviews

A number of works discuss the complementarity principle in great detail. The books and articles listed in this section offer a wealth of information not only with regard to the key elements of “unwilling” or “unable” but also on the permutations that complementarity has undergone since its adoption. Miskowiak 2000 offers an interesting early appreciation of the principle with an emphasis on distinguishing it from the subsidiarity principle. Arbour and Bergsmo 1999, Bergsmo 1998, and Benzing 2003 offer a clear, precise, and detailed analysis of the relevant statute articles, necessary for the appreciation of the achievement by the drafters at Rome, and an insight into the complexity of this fundamental concept. Furuya 2009, by contrast, with the benefit of time, provides a succinct exposition of the principle in general, focusing on the emerging practice by the International Criminal Court (ICC). Finally, in recent years a number of academic monographs have focused on exploring almost every aspect of complementarity. The two-volume collection Stahn and El Zeidy 2011 constitutes a major reference point for the treatment of the principle, both in terms of its theoretical underpinnings and with regard to its practical ramifications. Kleffner 2008 also offers an original conceptualization of the complementarity principle, focusing on issues of compliance and correctly emphasizing that complementarity has taken on a life of its own, beyond the strict jurisdictional principle envisioned by the drafters. Similarly, Stigen 2008 focuses on complementarity from a wider international law perspective and compares it also to the concept of primacy that governed the relationship with national courts of the ad hoc tribunals that preceded the ICC. The works below provide expert analysis of the complementarity principle as a whole and, as such, are key to the understanding of the wider ramifications of the principle.

  • Arbour, Louise, and Morten Bergsmo. “Conspicuous Absence of Jurisdictional Overreach.” International Law Forum du Droit International 1 (1999): 13–19.

    DOI: 10.1163/15718049920961864

    One of the first articles on complementarity, it offers an essential analysis of the then-new concept. It poses a number of challenging questions that are still relevant today, such as the meaning of unwillingness and the relationship between the ICC and the UN Security Council.

  • Benzing, Markus. “The Complementarity Regime of the International Criminal Court: International Criminal Justice between State Sovereignty and the Fight against Impunity.” Max Planck Yearbook of United Nations Law 7 (2003): 591–632.

    DOI: 10.1163/138946303775160250

    A well-written, yet somewhat descriptive exposition of the complementarity principle and the procedural framework in which it operates.

  • Bergsmo, Morten. “The Jurisdictional Regime of the International Criminal Court (Part II, Articles 11–19).” European Journal of Crime, Criminal Law & Criminal Justice 6 (1998): 345–363.

    The article provides short commentaries on each of the relevant Rome Statute provisions.

  • Furuya, Shuichi. “The Principle of Complementarity in Reality: Who Actually Applies It and in What Way under the ICC System?” In Public Interest Rules of International Law: Towards Effective Implementation. Edited by Teruo Komori and Karel Wellens, 293–312. Farnham, UK: Ashgate, 2009.

    A brief article that explores the ICC’s practice on complementarity in general.

  • Kleffner, Jann K. Complementarity in the Rome Statute and National Criminal Jurisdictions. Oxford: Oxford University Press, 2008.

    DOI: 10.1093/acprof:oso/9780199238453.001.0001

    National suppression of core crimes at the domestic level and its implications constitute the starting point for this monograph. The work provides an original conceptualization of the principle of complementarity as a catalyst for State Party compliance. The author further suggests that complementarity takes on a life of its own beyond the formal legal framework of the implementation rules.

  • Miskowiak, Kristina. The International Criminal Court: Consent, Complementarity and Cooperation. Copenhagen: DJØF, 2000.

    This book provides a short overview on complementarity and constitutes an early work on the subject. The distinction between complementarity and subsidiarity is particularly noteworthy (pp. 45–46).

  • Stahn, Carsten, and Mohamed M. El Zeidy, eds. The International Criminal Court and Complementarity: From Theory to Practice. Cambridge, UK: Cambridge University Press, 2011.

    A detailed collection of very interesting contributions on complementarity enhanced by insiders’ views from both the Office of the Prosecutor and the Registry. The book also focuses in great detail on the situations in Colombia, Darfur, Democratic Republic of the Congo, Uganda, and Kenya.

  • Stigen, Jo. The Relationship between the International Criminal Court and National Jurisdictions: The Principle of Complementarity. Leiden, The Netherlands: Martinus Nijhoff, 2008.

    DOI: 10.1163/ej.9789004169098.i-536

    A laudable effort to analyze the complementarity principle in a broad and inclusive manner. Particularly noteworthy is the last chapter of this book in which Stigen attempts to answer the question of whether primacy of the ICC over national courts would have been more desirable.

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