In this Article, the authors develop an economic theory of the constitutional amendment process under Article V focusing particularly on the roles that Congress and interest groups play in that process. The authors construct a model to predict when an interest group will seek an amendment rather than a statute to further its interests, highlighting how interest group maintenance costs and anticipated opposition affect that choice They then discuss the efficiency goals of constitutionalism-precommitment and reduction of agency costs--and argue that the structure of the amendment process under Article V prevents realization of these goals The authors contrast the Bill of Rights amendments, which established precommitments and reduced the agen...