In one of the most striking developments in American legal scholarship over the past quarter century, social movements have become central to the study of law. In constitutional theory, movements have emerged as key drivers of legal reform, creating new constitutional ideals and minimizing concerns of activist courts overriding the majority will. In lawyering theory, movements have appeared as mobilized clients in the pursuit of social change, leading political struggle and shifting attention away from concerns about activist lawyers dominating marginalized groups. In a surprising turnabout, social movements—long ignored by legal academics—have now achieved a privileged position in legal scholarship as engines of progressive transformation. Why social movements have come to play this dramatic new role is the central inquiry of this Article. To answer it, the Article provides an original account of progressive legal theory that reveals how the rise of social movements is a current response to an age-old problem: harnessing law as a force for social change within American democracy while still maintaining a distinction between law and politics.