This essay reviews two books suggesting how international investment law may be recalibrated to balance the interests of foreign investors and host states. Poulsen’s book draws mainly on empirical research to argue that developing states displayed ‘bounded rationality’ when rushing to sign up to investment treaties incorporating pro-investor protections, such investor-state arbitration. Although mainly descriptive, it sketches potential reforms of the investment treaty system to achieve a more rational balance in favour of host states. By contrast, drawing on doctrinal analysis but with a keen awareness of the institutional underpinnings of international investment law and arguably analogous fields, the book by Henckels focuses on what arbitrators and commentators can do to extend a tendency to interpret substantive protections even within existing investment treaties in a more balanced way. She urges more consistent application of multi-layered ‘proportionality’ analysis, combined with principled ‘deference’ to regulatory decision-making by host states.