Recent years have seen a trend towards increasing transparency in international investment arbitration. This trend has been reflected in arbitral practice and in the amendments to the ICSID Arbitration Rules in 2006, which now expressly allow for participation of non-disputing parties as amicus curiae. Still more problematic, however, is the publication of arbitral documents, which has recently been controversial in Biwater Gauff v. Tanzania. This paper will discuss the core provisions on the publication of documents of the UNCITRAL Arbitration Rules, the ICSID Arbitration Rules and NAFTA Chapter 11. It will analyze the reasoning and the findings of the Biwater Tribunal in this regard as well as the pertinent practice of previous investment tribunals. Important policy issues underlying the decision of the Biwater Tribunal will also be analyzed.