Populism in relation to constitutionalism is a widely discussed and critical, topic. In the literature on the phenomenon, there is a prevalence to identify populism as antithetical to constitutional democracy and as eroding the idea and fundamentals of constitutionalism. However, as this chapter will show, much depends on the definitions offered of populism and constitutionalism, and the analytical commitment to study both as historical phenomena with important contextual differences. As I will argue in this chapter, constitutionalism as such is a contested phenomenon, and populism frequently takes up different forms of critique on the predominant legal understanding of constitutionalism. Furthermore, populism is a phenomenon that manifests itself in different ways, displaying diverse guises depending on distinctive ideological position (left- or rightwing), but equally showing variety in terms of positioning regarding characteristic issues, such as sovereignty, the definition of the political community, or relations to constituent power.