What Is ICC Complementarity? Why It Is a Court of Last Resort

Complementarity is the principle that the International Criminal Court is a court of last resort. It may step in only when a country’s own courts are unwilling or genuinely unable to investigate and prosecute the crimes themselves.

The rule

Under Article 17 of the Rome Statute, a case is inadmissible before the ICC if a state with jurisdiction is genuinely investigating or prosecuting it. National courts have the first right — and duty — to act.

"Unwilling or unable"

The ICC can proceed only if it finds a state unwilling (e.g. shielding a suspect through sham proceedings) or unable (e.g. a collapsed justice system). This is why states facing ICC scrutiny often point to their own investigations.

Why it matters

Complementarity keeps primary responsibility with states and prevents the ICC from being flooded. It also means the key legal fight is often admissibility — whether genuine domestic proceedings exist — as much as guilt or innocence.

Frequently asked questions

Does a domestic investigation always block the ICC?

No. It blocks the ICC only if the proceedings are genuine. Sham or delayed investigations designed to shield a suspect do not satisfy complementarity.

Who decides if a state is "unwilling or unable"?

The ICC’s own judges, in an admissibility ruling, applying the criteria in Article 17 of the Rome Statute.

Primary sources

• Rome Statute — Article 17 (admissibility)
• ICC — how the Court works