Modern constitutional doctrine is full of restrictions on the reasons for which legislatures can enact certain kinds of statutes. Modern American courts, moreover, stand ready to enforce those restrictions by considering a broad array of sources about the hidden purposes behind challenged statutes. Yet for most of our history, courts shied away from those inquiries—not because state and federal constitutions were thought to impose no purpose-based restrictions on legislative power, but because such restrictions were not thought to lend themselves to much judicial enforcement. This Article calls attention to bygone norms of judicial review, which often prevented courts from investigating the motivations behind statutes even when the statutes’ constitutionality depended upon those motivations. The Article proceeds to describe changes over time in the practice of judicial review. The history that emerges sheds light on myriad subjects, including the proper interpretation of various seminal precedents, the source of some of the apparent inconsistency in doctrines that implicate purpose-based restrictions on legislative power, and the ways in which uncodified aspects of judicial practice can affect the glosses that courts put on the Constitution’s text.