As with everything which cannot be seen or grasped, customary law remains something of a smiling sphinx in the realm of legal theory. Over the centuries, it has tended to generate puzzling questions of understanding and of construction, some linked to the concept of custom itself, others linked to the conception of custom within the context of a specific society with its special structure. In societies where custom continues to play a paramount role, that is, in societies deprived of a centralised legislator, the predominance of custom imports into the law and law-making the many uncertainties invariably linked with it. This is particularly true of international law. The objective of this short contribution is to address some of these problems in the form of brief commentaries following a concise statement of the point or problem at issue.