When we interpret customary international law (CIL), what is it that we actually interpret? The most promising option is that interpretation of CIL is an interpretation of legal practices. However, the dominant two-element doctrine of CIL assumes that opinio juris generates both legality and normativity of practices, when the latter have no independent normative significance. The chapter challenges this view by drawing on jurisprudential ideas that define practices as inherently normative. This view allows to differentiate between two instances of interpretation of CIL. One is focused on clarification of the normative content of state practices, another is focusing on identification of these practices as legal ones. Interpretation as clarification involves assessing structures of practical reasoning. Interpretation of CIL implies establishing connections between first- and second-order reasons that form the practice and give it meaning. This entails that interpretation of CIL focuses on dynamics of reasons, their inclusion and exclusion within an existing normative framework. Interpretation as identification involves showing that existing second-order reasons meet a threshold of legal validity, which may take the shape of opinio juris, but may as well be functional, when legality of a practice is linked to its relevance in a broader set of legal practices