The jurisprudential dimensions of treating custom as law have been puzzling at least since the time of Bentham and Austin. If law emanates from the sovereign, and consists of commands backed by threats from the sovereign, then customary law seems scarcely law at all. Or so Bentham and Austin, each in his own way, believed. But if, in a post-Hart jurisprudential world, we can recognize that norms can be internalized by judges and other officials even if they arise from the bottom up rather than from the top down, then a new puzzle emerges. In this modern jurisprudential world, the lawness of custom can easily be explained, but custom then appears simply to be one of many forms of law, occupying no distinct juridical space. The question whether and when to treat custom as law, therefore, is no different from the question whether and when one jurisdiction treats another jurisdiction’s norms as law, and whether and when to treat some particular source as law. These are important and sometimes difficult issues, but they are more continuous with the routine questions of legal sources and legal authority than the traditional treatments of custom have assumed.