Volume III of the Cambridge History of Law in America covers the period from 1920 to the present, ‘the American Century’. It charts a century of legal transformations - in the state, in legal thought and education, in professional organization and life, in American federalism and governance, in domestic affairs and international relations. It shows how, politically, socially and culturally, the twentieth century was when law became ubiquitous in American life. Among the themes discussed are innovation in the disciplinary and regulatory use of law, changes wrought by the intersection of law with explosive struggles around race, gender, class and sexuality, the emergence and development of the particularly American legal discourse of ‘rights’, and the expansion of this discourse to the international arena. The main focus of this last volume of the Cambridge History of Law in America is the accelerating pace of change, change which we can be confident will continue. The Cambridge History of Law in America has been made possible by the generous support of the American Bar Foundation.