This chapter considers how cognitive studies can inform and augment constructivist approaches to international law. The central argument is that research into the working of the human mind and inter-group relations helps to explain how the institutional environment in which rules are developed and interpreted shapes the legal positions of states. States send signals to one another, they negotiate, they argue, and they engage in diplomatic conversation about international law—how it is made, interpreted, and implemented. Accordingly, this chapter considers how cognitive studies can help to explain the argumentative behavior of government officials and other international actors associated with a particular type of “community of practice,” namely interpretive communities. It identifies avenues for improving the design of legal regimes and institutions to address biases and heuristics associated with individual and group decision-making. The chapter emphasizes the importance of mechanisms that stimulate reasoned deliberation as opposed to purely intuitive and/or “automatic” cognition in global governance institutions. A case study of cybersecurity regime-building is used to highlight both the value and limitations of cognitive studies in understanding international legal argumentation and interpretation.