The concept of trust will be scrutinized across different and sometimes antagonistic genres of international political thought. The natural law tradition and reason of state tradition worked on different assumptions, but they mutually influenced each other. How have these traditions influenced the different concepts and discussions of trust-building? The programmatic theorising by eighteenth-century thinkers of trust shows that there was not just one coherent argument of trust, but that trust was placed in different conceptual contexts, in which its meaning and importance changed accordingly. There was thus not one straightforward evolution of the argument, but a range of conflicting arguments that used trust differently. Balance of power thinking discussed trust as purely strategic, whereas the proponents of designs for peace proposed institutional solutions to make trust among states possible, because they perceived trust as foundational for overcoming the inherently antagonistic relations between sovereign states. Despite the ongoing search for conditions of trust between states, we are today still faced with the same structural problems.