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The principle of complementarity is the basis of the relationship between the International Criminal Court (ICC) and national courts in relation to the application of international criminal law

The principle of complementarity is implemented by the ICC through Articles 17 and 53 of the Rome Statute, it provides that a case is inadmissible before the ICC if it is currently under investigation by a state with jurisdiction over it. The concept of complementarity, however, allows for ICC jurisdiction in situations when the state is unable or unwilling to proceed with an investigation or where the state investigation is conducted in bad faith such as when it is used to shield the person from criminal responsibility. 

In other words, States have the primary competence and authority to investigate and prosecute international crimes, and the ICC has secondary jurisdiction. Given that complementarity is assessed on a case-by-case basis, the ICC and states must together ensure that all atrocities in each situation are addressed.

[Last updated in October of 2022 by the Wex Definitions Team]