The paper develops an economic theory of the Chilean Constitution and the legislative process, and the role that play interest groups in the later. For the authors is not clear that the only approach when analyzing interest group politics consists, inevitably, in establishing statutory regulations, like campaign finance laws and lobbying regulation. To the contrary, this paper suggests that the Chilean Constitution and the design of the legislative process should be considered more seriously. Different constitutional principles, institutions and mechanisms are established in the Chilean constitutional design that raises the costs of capturing the State and Congress. Thus, the authors propose an economic theory of the Chilean constitution and analyze different topics such as the bicameral system, executive veto, delegation of legislative powers to the Executive and the legal reserve clause, the respect for the matrix ideas of a legislative proposal, quorums, judicial review of legislation by the Constitutional Court, among others.