The question of the right of appeal by third parties raises significant issues in the field of arbitration. Such issues relate, firstly, to the very principle of allowing a third party to bring an appeal (“tierce opposition”). As much as this does not give rise to any particular issue when the decision in question is a state decision rendered in relation to arbitration, it does raise concerns when it comes to arbitral awards. Indeed, it may be questioned whether denying third parties a right of appeal in the international field is in line with requirements of due process. Alongside general concerns as to admissibility, particular issues arise when it is an arbitrator or an arbitral institution which seeks to assert its right of appeal.