This chapter begins from the proposition that the conventional narrative suggests that there are unwritten constitutional rules and principles that exist adjacent to, or supplementary to, the official written constitution. But the spatial metaphor suggested by this framing of the issue is mistaken, the author says. He notes that we have learned from the enduring jurisprudential contributions of Hans Kelsen and H. L. A. Hart that the status as law of a constitution rests on a necessarily unwritten social practice establishing what counts as the constitution. This unwritten social practice might exclude some of what the official written document includes and might include some rules or principles that are not found in the official written document, but the basic point is that a written document’s status as “the constitution” rests itself on unwritten foundations, making the idea of an unwritten constitution central to the very idea of constitutionalism.