This chapter addresses a new and fertile research program: constitutional law and economics. Constitutional law and economics asks questions like, ‘What is the extent of the U.S. Congress’s power to regulate commerce?’; ‘How much legislative authority can be delegated to administrators?’; and ‘When should constitutional change happen through judicial updating rather than formal amendment?’ To address such questions, constitutional law and economics blends positive, normative, and interpretive analysis. This chapter describes all three but emphasizes interpretation. After introducing these modes of analysis, we turn to constitutional law. Six processes make and sustain constitutions: bargaining, voting, delegating, entrenching, adjudicating, and enforcing. Economic theory illuminates these processes, and constitutional law reflects them. We showcase the potential of constitutional law and economics by applying it to concrete problems.