Much has been written on the legal status of customary law, but considerably less attention has been devoted to the question of determining the content of the customary law whose legal status (or not) is at issue. Like any other source of law, customary law presents the question of interpreting, applying, and enforcing the emanations from that source, but interpreting customary law – or interpreting the custom that is to be part of the law – presents issues arguably more complex than those presented when we are considering the interpretation of constitutions, statutes, regulations, treaties, and even the common law. My goal here is to explore these interpretive questions, and to do so with perhaps somewhat of a skeptical attitude. This is not to say that such skepticism will turn out at the end of the day to be justified. It is to believe, however, that addressing such skeptical questions is an inevitable task for any satisfactory account of the role of customary law in common law adjudication, and perhaps to an even greater extent with respect to the role of customary international law as a part of international law more generally. So, although in this paper I will ask more questions than I answer, my goal is to put on the table those interpretive issues that anyone seeking to develop a theory of customary international law, or a theory of the role of custom in common law decision-making, must at least attempt to answer.