This article addresses the power of law to make historical change. We begin by charting a rich debate on law’s autonomy held over the course of the twentieth century, overviewing contributions by Classical Legal Thought, Law and Society, Marxism, the New Left, Critical Legal History, and what we term the “Millennial Consensus.” We then sketch an alternative view that we feel is implicit in much legal history, where the law is seen as an “architecture”—a set of tools with which we build our society. On this view, law’s autonomy lies in the way that it facilitates specific forms of societal ordering at the expense of others. We emphasize that it also has an existential dimension in that we can never foresee all the future uses particular legal institutions may be put to.