Performance requirements act as policy instruments for achieving broadly-defined economic and developmental objectives of States, especially industrial and technological development objectives. Many States consider that performance requirements distort trade and investment flows, negatively impact global and national welfare and disrupt investment decisions compared to business-as-usual scenarios. As a result, a number of States have committed to prohibiting performance requirements in international investment agreements (“IIAs.”). Performance requirement prohibitions (“PRPs”) are meant to eliminate trade-distorting performance requirements and performance requirements which replace investor decision-making by State decision-making. This thesis focuses on providing answers to two research questions: first, how do States prohibit performance requirements in IIAs? And second, how should PRPs in IIAs be interpreted and applied? For the first time, this thesis: proposes a comprehensive understanding of PRPs in IIAs by drawing notably on the General Agreement on Tariffs and Trade (“GATT”) Uruguay Round of negotiations and on the United States Bilateral Investment Treaty (“BIT”) Programme; develops a detailed typology and analysis of PRPs in IIAs through the identification of systematically reproduced drafting patterns; conducts the first critical and in-depth analysis of all arbitral awards which have decided claims based on PRPs in IIAs; analyses interpretation and application issues related to provisions that exempt government procurement from PRPs and to reservations that shield sensitive non-conforming measures or strategically important sectors from PRPs; and anticipates the application of most-favoured nation (“MFN”) treatment clauses to PRPs in the future. Finally, this thesis formulates proposals that can help interpret and apply existing PRPs and draft future PRPs in a more deliberate and informed way.