This article develops a socio-legal approach to theorizing the construction of peremptory norms in international relations. It argues that due to its focus on formalism and abstract notions of rights, traditional legal treatments have failed to acknowledge the socially constructed nature of higher order norms. To address this shortcoming, the article transfers the concept of jus cogens into the realm of International Relations. Drawing on insights from constructivism and English School theory, it situates law in the context of society and conceptualizes jus cogens as part of international society’s constitutional structure. Proceeding from the assumption that the content and identity of jus cogens depends on the normative character of international society, the article then assesses two possible ‘normative logics’ through which the peremptory status of a norm may be generated. It rejects a solidarist logic, which sees universal norms as the manifestation of cosmopolitan ideas about inalienable rights. Instead, it argues for a pluralist approach to ethics and order that depicts jus cogens as key to the development of international society towards a social site marked by diversity and respect for difference.