Even if the Court’s jurisdiction has been properly triggered and the Prosecutor has decided to conduct an investigation, a given case may be declared inadmissible in three circumstances: the State that normally exercises jurisdiction is actively investigating or prosecuting, the case is not of sufficient gravity, and the accused has already been tried for the offence (ne bis in idem). The first of these circumstances is described by the term ‘complementarity’. Its underpinning is the notion that States are primarily responsible for prosecution and the Court intervenes only when they are unwilling or unable to prosecute, or inactive. Although judges may determine that a case is not of ‘sufficient gravity’, in practice this criterion has been invoked mainly by the Prosecutor in order to justify decisions not to proceed with preliminary examination or investigation.