Customary international law is an enigma It is produced by the decentralized actions of states, and it generally lacks centralized enforcement mechanisms. Political science realists and some rationalist legal scholars argue that customary international law cannot affect state behavior: that it is\epiphenomenal.\ This article develops a model of an n-player prisoner's dilemma in the customary international law context that shows that it is plausible that states would comply with customary international law under certain