On March 4th, 2009, the Pre-Trial Chamber (PTC) of the International Criminal Court (ICC) issued an arrest warrant against Omar Hassan Al-Basir, the Sudanese President in relation to the alleged crimes committed in Darfur. The decision constituted the first precedent in which the question of state immunity has been raised before the ICC and the first time an international criminal tribunal has indicted an incumbent head of state. This article aims to clarify the legal aspects of the arrest warrant and the status of head of state immunity in customary international law in order to assess the applicability of the immunity of heads of state before international criminal tribunals, in particular the ICC. This is done by examining the decision of the PTC as to whether the immunity enjoyed by President Al-Bashir precluded proceedings before the ICC. The article also discusses the obligation of Sudan, as a non- state party to Rome statute, to comply with the Court’s request for cooperation in the execution of the arrest warrant.