This article collects data on fair and equitable treatment (FET) ‘elements’ from ISDS awards and investment treaties, respectively, and examines the extent to which States incorporate ISDS tribunals’ interpretation of FET into their subsequent design of treaty clauses. According to the empirical findings, States do incorporate tribunals’ interpretations in treaty design; nevertheless, the practices of incorporation vary according to the types of elements and the economy classification of treaty parties, and are subject to constraints such as bounded rationality and institutional capacity. The findings also reveal the substantive divergence between treaties and the ISDS jurisprudence in the enumeration of FET elements, which, I caution, may exacerbate legitimacy challenges against ISDS.