The chapter introduces the diversity of epistemological and ontological perspectives within constructivist research in order to explore existing links between Constructivism in IR and scholarship on Global Constitutionalism as well as potentials for further research. I argue that Critical Constructivism offers crucial analytical value to the study of Global Constitutionalism since it not only allows for a broader understanding of constitutionalisation and seeks to dissect meaningful action of actors, but also problematises the production of knowledge and the processes of observation by researchers. Further, the chapter outlines how Constructivism’s work on norms, normativity and order is central to understand constitutionalisation.