This chapter examines the issue of transparency in treaty-based investment arbitration by focusing on the participation of third parties or non-disputing parties in disputes. More specifically, it considers the procedural issues that transparency mechanisms in bilateral-investment treaties and free-trade agreements, as well as in recently revised arbitral rules, create for arbitral tribunals and those appearing before them. After discussing non-disputing party practice in investment arbitrations, the chapter explains the practice of non-disputing state parties in UNCITRAL and International Centre for Settlement of Investment Disputes (ICSID) arbitrations. It also analyses transparency mechanisms beyond the participation of non-disputing parties in investment arbitrations from the written procedure through to the oral procedure, culminating in a tribunal's decisions and award.
