The role of domestic courts in the application of international law is one of the most vividly debated issues in contemporary international legal doctrine. However, the methodology of interpretation of international norms used by these courts remains underexplored. In particular, the application of the Vienna rules of treaty interpretation by domestic courts has not been sufficiently assessed so far. Three case studies (from the US Supreme Court, the Mexican Supreme Court, and the European Court of Justice) show the diversity of approaches in this respect. In the light of these case studies, the article explores the inevitable tensions between two opposite, yet equally legitimate, normative expectations: the desirability of a common, predictable methodology versus the need for flexibility in adapting international norms to a plurality of domestic environments.