Whenever two legal systems or regimes can each exercise jurisdiction over the same issues, some mechanism will usually be developed in order to determine which one proceeds first. In the case of genocide, crimes against humanity and war crimes, the International Criminal Court operates in parallel with national justice systems, which are also positioned to prosecute the offences in question. The underlying premise of the Rome Statute is that, when national justice systems fail, the International Criminal Court steps in, as a last resort so to speak. The preamble to the Rome Statute recalls that ‘it is the duty of every State to exercise its criminal jurisdiction over those responsible for international crimes’. Consequently, Article 17 of the Statute prescribes that the Court may take on a prosecution only when national justice systems are ‘unwilling or unable genuinely’ to proceed. The Statute addresses the issue under the rubric of ‘admissibility’. The Court may well have jurisdiction over a case, in the sense that the alleged international crime was committed subsequent to 1 July 2002, on a territory of a State Party to the Statute, or by a national of a State Party, or where there has been a Security Council referral or a declaration accepting jurisdiction by a non-party State. But, if the case is being investigated or prosecuted by a State with jurisdiction over the crime, the Prosecutor must demonstrate that it is ‘unwilling or unable genuinely’.