States exhibit various commitments problems in creating international legal rules and institutions. International law is needed to solve collective action problems such as climate change, manage common pool resources, maintain peace, and realize justice. The paradox of commitment explains some of these commitment problems. States would benefit from more effective rules which reduce conflict, enable cooperation and coordination, and resolve collective action problems, but they are reluctant to restrict their own freedom in the name of those rules and the institutions tasked with interpreting and enforcing them. Constitutionalism is available as a language and process which can inform mechanisms for reducing states’ commitment problems. Drawing on legal philosophy, constitutional theory, and empirical social science, I propose to consider a form of global constitutionalism which encourages states to pre-commit to certain basic principles of international cooperation, institutions, and decision-making procedures. Without constitutional rules, international politics falls prey to power politics, vulnerable states are swept up by the brute force and inertia of the big military and economic powers, rule of law protections for states and individuals are weak, human security is at risk, and the threat of violence remains ubiquitous as the primary means of structuring the interaction among states.