This article offers a way of more fully understanding the nature of the United States constitution. It advances a perspective of constitutional realism, drawing on the American legal realist tradition, that emphasizes the importance of identifying the reality of how public power is exercised. The resulting conception of a “complete constitution” extends to the structures, processes, principles, rules, conventions and even culture that constitute the generic ways in which public power is exercised. The article undertakes a comparative analysis of the reality of a paradigmatic real-world unwritten constitution – that of New Zealand. It then suggests how such an analysis can be undertaken in the United States. It calls for greater attention to be paid to identifying and analyzing the important elements of the “complete” U.S. constitution that do not exist in the text so-labelled, including those elements that may exist in beliefs and behaviour. Changes to these constitutional elements deserve levels of scrutiny and national dialogue that should be just as intense and considered as changes to the text of the Constitution. The current incomplete American conception of the U.S. Constitution means that may not occur.