The PCA Secretary-General’s role to designate or act as an appointing authority has been the sole institutional mechanism in the otherwise ad hoc UNCITRAL Arbitration Rules since their adoption in 1976.While the UNCITRAL Arbitration Rules provide that jurisdictional objections shall be decided by the arbitral tribunal once constituted, they say nothing about what the PCA should do when faced with a jurisdictional objection prior to tribunal constitution. In practice, the PCA has applied a prima facie standard for arbitral jurisdiction in deciding whether an arbitral tribunal should be constituted. The cases described in this article offer examples of how the PCA conducts this prima facie review and its consequences for subsequent decisions on arbitral jurisdiction by arbitral tribunals and national courts.