International investment arbitration remains one of the most controversial areas of globalisation and international law. This book provides a fresh contribution to the debate by adopting a thoroughly empirical approach. Based on new datasets and a range of quantitative qualitative and computational methods the contributors interrogate claims and counter-claims about the regime''s legitimacy. The result is a nuanced picture about many of the critiques lodged against the regime whether they be bias in arbitral decision-making close relationships between law firms and arbitrators absence of arbitral diversity and excessive compensation. The book comes at a time when several national and international initiatives are under way to reform international investment arbitration. The authors discuss and analyse how the regime can be reformed and ow a process of legitimation might occur.