This Chapter examines the treatment of foreigner s with an emphasis on the notion of ‘fairness’, highlighting its evolution from a subjective and contingent consideration guiding sovereign discretion, to an ostensibly objective international standard commonly referred in contemporary international investment law. With increased inter-communal interactions and the development of international law from the seventeenth century onward, a vague, yet influential international standard began to take shape, replacing more provincial, contingent conceptualisations of fairness. Despite its controversial foundation, the so-called international minimum standard (IMS) remains a key principle in international investment law today, influencing international adjudication and treaty-making practices of states. The analysis constructs the theoretical framework for the rest of the book, and underscores the necessity for more inclusive and clearly defined global rules guiding substantive protection principles in international investment law.