Investor–State arbitration makes an important contribution to increasing international investment fl ows by, inter alia, mitigating political risk for investors. Th is mixed international arbitration in turn relies on the obligations of States, which are embodied in bilateral investment treaties and customary international law. A key technique used in bilateral investment treaties to achieve protection for foreign investors has been to include a requirement that a host State provide ‘fair and equitable treatment’ of foreign investments within its territories. One of the key, controversial, issues in mixed international arbitration has been the extent to which a State’s compliance with the requirement of fair and equitable treatment should be evaluated according to the customary international minimum standard of protection, or rather according to a national, often lower, standard. Th is extremely well-researched contribution by Dr Paparinskis makes crucial contributions to our understanding of the relationship between these two key concepts of foreign investment law, and in so doing also provides invaluable insights into the contemporary content of both concepts.