This chapter defines traditionalism in American constitutional law, drawing from the rich deposit of the common law as an analogy to what the Supreme Court is now doing in constitutional law. It identifies traditionalism’s components in three elements: (1) political practices (2) of long duration that (3) are given presumptive authority in determining the law of the Constitution. It concludes by arguing that the method is actually of much longer lineage than one might think if one only looked at Supreme Court cases of the last few years.