This chapter examines the constitutional role of parties and partisanship. We begin by sketching a conception of constitutionalism as a mechanism for finding an equilibrium between different social interests. Appealing as this ideal of moderation has long been for many, we highlight its limits as a basis for democracy and progressive change. A desirable constitutional model must make space for political conflict and immoderation, and as we go on to argue, partisans and the associations they form are an important foundation for this. The final section connects these observations to the contemporary political world, in particular to the state of parties today and to some of the misplaced anxieties about ‘polarisation’ they give rise to.