Back in December 2010, Mauritius initiated proceedings against the United Kingdom challenging the establishment of a Marine Protected Area (MPA) around the Chagos Archipelago as a violation of the 1982 United Nations Convention on the Law of the Sea. Mauritius is expected to argue that the United Kingdom had no right to establish an MPA because it does not have sovereignty over the archipelago. Yet, the establishment of the arbitral tribunal under Annex VII of the 1982 Convention has been delayed by a challenge raised by Mauritius against the arbitrator nominated by the United Kingdom, namely Judge Sir Christopher Greenwood. A decision rejecting the challenge was given by the tribunal back in October 2011, but the reasoned decision of the tribunal has just been posted on the website of the Permanent Court of Arbitration and it offers an interesting read. Challenges to individual arbitrators in inter-state arbitration are rare. Indeed, there have been no known cases where an arbitrator has been challenged in an arbitration brought under the 1982 United Nations Convention on the Law of the Sea. This decision is important as it provides a first attempt to clarify the rules and principles which apply in this situation.