The investment treaty arbitral tribunals had experienced a significant increase in the disputes initiated for noncommercial activities, such as environmental protection, public health, human rights and labour standards. It has witnessed the greater participation of civil society as non-disputing parties to gain access to these forums as amicus curiae. Initially, none of the international investment instruments had explicitly authorized the submission of amicus curiae briefs. It was only after 2001 when the NAFTA tribunal accepted amicus curiae briefs in the most celebrated case of Methanex, which was followed by the UPS and the Glamis disputes, it is emerging as a practice in the investment treaty arbitration. The ICSID tribunal also admitted amicus briefs on the basis of public interest for the first time in the Vivendi case on 19 May 2005, followed by the Aguas Provinciales in 2006 for the purpose of distribution of water. As an outcome of this Tribunal, the ICSID Arbitration Rules were amended to incorporate an explicit provision to approve amicus curiae briefs. The acceptance of amicus briefs clearly shows the interest of the common public in the process of investment arbitration. Most of the scholars welcomed the arrival of non-disputing parties in the ICSID and the UNCITRAL arbitrations. But, the confidentiality of proceedings remains as a general rule. Amicus-curiae are refused to access documents and to attend hearings unless disputing parties consented to do so. This practice apparently raised a serious doubt on greater transparency and equal participation of non-disputing parties in arbitral proceedings. It is in this connection, the paper makes a concerted attempt to address the pertinent issues involved in participation of amicus curiae in arbitral proceedings. It further looks into the details on various issues on access to information, publication of awards and the admissibility of amicus curiae briefs.