Persona non grata declarations under international diplomatic law

The power to expel foreign diplomats is an important diplomatic instrument for states to defend their interests, including the protection of their national security. This article gives an overview of various aspects of the public international law institution of persona non grata declaration, which is governed by article 9 of the Vienna Convention on Diplomatic Relations (1961). It is argued that international law imposes few constraints on the receiving state issuing a persona non grata declaration.