How can states influence the formation and functioning of international legal institutions they are party to? Do international legal commitments influence domestic politics? Throughout five articles, I examine these questions within the bounds of the international investment treaty regime. Using unique qualitative and quantitative data, I find that both state capacity as a structural factor and the expertise and skills of individual negotiators, are crucial for states’ ability to make their mark in interstate negotiations, and that state capacity is associated with states' domestic responses to international legal challenges brought by foreign investors.