This chapter relies on original archival research to inform the evolution of contractual protection in international law. Before investment treaties emerged as instruments of contractual protection, investors sought diplomatic protection from their home states in contractual disputes with host states. At first glance, the shift from diplomatic protection to treaty protection in contractual disputes between investors and states, and the different considerations each entails, discounts the contemporary relevance of historical findings. However, despite significant changes over time in the mode of securing contractual protection, reservation towards the characterisation of simple contractual breaches by states, such as non-payment, as violations of international law remains. This chapter suggests that the scepticism exhibited by modern-day adjudicators towards the capacity of open-textured investment treaty provisions to equate simple contractual breaches with violations of international law, is a product of the historical reluctance of states to endorse this equation.