This chapter teases out the different theorisations – or conceptual frameworks – of the EEAS in order to show how they – whether implicitly or not – make a difference to our understanding of the EEAS. The chapter first provides an overview of existing approaches to the EU’s diplomatic service, examining specifically two main approaches to the EEAS: the rationalist approach (including intergovernmentalism, rational choice institutionalism and rationalist organisation theory) and the constructivist approach (including sociological institutionalism and sociological organisation theory). The chapter then demonstrates how these approaches paint contrasting portraits of the EEAS: as a rational political player seeking autonomy from its principals (the member states) or as a social body or organisational arena with norm-abiding civil servants trying to make sense of the new diplomatic world. These theoretically informed portraits of the EEAS build on different assumptions about the nature of European integration, diplomacy and social science. The chapter points to possible blank spots on the map and the potential contribution of approaches currently not widely adopted in the study of the EEAS, including legal-constitutional frameworks, diplomatic theory, network theory, practice theory, anthropology and democratic theory.