Semi-presidential regimes have attracted increasing attention from scholars and constitutional reformers over the last quarter century. Yet, despite this popularity, there is no consensus on how to understand this constitutional format. Since Duverger defined semi-presidentialism as a new political system model, and Linz argued that the constitutional format shares many of the perils of presidentialism, subsequent research has questioned the conceptual status of semi-presidentialism as a distinct regime type, and whether it has any distinct effects on politics. In this article we review the progress of recent work on semi-presidentialism and suggest that the conceptual tools to clarify some of the major debates in the field are now available in the form of principalagent theoretical work on democratic constitutions. © 2009 Cambridge University Press.
