This book addresses the role of investment arbitrators within the framework of international investment law, a system that tends by design to prioritise the interests of foreign investors, often at the expense of the economic and social policies of the host states. The theoretical foundations of this volume are doctrinal, and the argument presented is aimed at contributing to the scholarly debate on the reform of the system of investment law. Because of this, the book is particularly focussed on the scholarship and is aimed at an audience already familiar with the system of investment arbitration and its case-law. The author explores both the explicit and implicit duties of arbitrators and critically questions certain critiques of investment law that call for arbitrators to interpret bilateral investment treaties and free trade agreements in ways that also protect the host states' interests. While the author argues that challenges to the legitimacy and credibility of the current investment law regime are well-founded, he also argues that arbitrators find themselves constrained by the prevailing legal framework, unable to fully balance the competing interests of foreign investors and host states. The book concludes that achieving greater equality in the investment legal regime necessitates a departure from the existing bilateral investment treaties paradigm and calls for a more just and balanced system of investment treaties. The author argues that, until such a transformation occurs, arbitrators remain compelled to apply the current applicable law, highlighting the insurmountable limitations and tensions within the present system.