This chapter examines constitutionalism in the United States, with particular emphasis on its origins and the problems of constitutional failure. It begins with an overview of the origins of constitutionalism, from the ancient period to the Middle Ages and through the modern times. It then describes the characteristics of constitutionalism in the United States, focusing on the debates over the locus of the Constitution’s authority, the legitimacy of judicial review, and the phenomenon of constitutional change. It also discusses critical theories that have set themselves against aspects of U.S. constitutional norms or practices, if not against constitutionalism itself. Two types of critical scholarship are considered: the first radically questions whether the very direction and constraint that constitutionalism demands or presupposes are possible, and the second includes theories that view the Constitution as an instrument for establishing or preserving certain hierarchies, whether of class, race, or sex (or all three).