Legislative scholars are very good at explaining and analysing what legislatures do and how they do it. But the why question – why legislatures do what they do and why they matter – is often taken for granted or not even raised at all. Our objective in this paper is to focus attention back onto the 'why' question and to explore the grounds upon which legislative scholars, and others, might be encouraged to reconsider this basic question. In seeking to coax a reconsideration of the importance of legislatures, we direct attention towards processes of legitimation and why legislatures are invested in such processes across the world in the modern era. If, as we argue, an answer to the question of why legislatures matter is to be grounded in processes of legitimation, then deficiencies in those processes or the questionability of those processes also expose the contingent nature of such an answer.