This book offers theoretical arguments and original empirical data on the legitimacy of the investor-state dispute settlement system in the eyes of the general public. The legitimacy of the investor-state dispute settlement (ISDS) system has become a major issue in recent negotiations on new trade and investment agreements, such as the Transatlantic Trade and Investment Partnership (TTIP), the Comprehensive Economic and Trade Agreement (CETA), and the Trans-Pacific Partnership Agreement (TPP). This book considers the remarkable rise of investor-state arbitration, its politicization and the corresponding legitimacy crisis that has induced a political process of ISDS reform. The book applies theoretical arguments about legitimacy perceptions among the mass public and tests these arguments in survey experiments in Germany, France, and the US to answer the question of whether ISDS reform can be successful. By showing that large parts of the population hold negative perceptions about the current system of private arbitration and believe that an international investment court and domestic courts are more legitimate dispute resolution systems, the book extends the debate on the legitimacy of the ISDS mechanism, which has so far been dominated by conflicting normative claims of supporters and critics. With regard to the academic debate about legitimacy in global governance, the author underlines that the legitimacy perceptions of ordinary citizens must be taken seriously to ensure the sustainability of global governance and international law in the long term. This book will be of interest to academics working in international relations, international political economy, international law, transnational law, authority, politicization, and legitimacy of global governance. It will also be of great use to practitioners in the field of international investment law, including lawyers, and government officials working in international dispute settlement.