This article argues that constitutional theory requires the concept of ‘constitutional office’ to theorize the place of the legislature. ‘Constitutional office’ is both distinct from, and complementary to, the more familiar concept of ‘institutional role.’ ‘Institutional role’ is a predominantly descriptive concept that is used to define the domain of legislative power. By contrast, ‘constitutional office’ is an irreducibly normative concept that goes to the manner in which legislative power is exercised. In this respect, the article argues, the concept promises to offer new analytical tools for advancing central debates in constitutional theory.