This thesis proposes a new way of addressing two central questions in the study of the European Union: What is the nature of the European Union as a political entity and how does it emerge? The point of departure is the, by now widely accepted, conceptualisation of the EU as a polity and the extensive discussions, not least in normative and prescriptive terms, that this process implied. Judging that many of the debates have reached dead-ends, the thesis proposes a novel way of conceptualising the concept ‘polity’ in its application to the European Union. It argues that the European Union polity should be understood as a configuration of agreements to collectively address common problems. The thesis then offers an analysis of three such fields of agreed upon common activities over the period 1992 to 2005 which are constitutive of the European Union polity and construct its boundedness: ‘Enlargement to the East’; ‘Immigration policy’; and ‘Europe as an actor in the world.’ Under scrutiny includes: the context in which these policies emerged; the normative ideas through which the problems at stake were identified; and the agreed-upon mechanisms for addressing common problems. To understand the emergence and nature of these common activities, the thesis proposes a concept-centred approach. It argues that concepts are constitutive for the European Union polity. The concepts constitute the agreements to address problems in common and thus ‘form’ the European Union polity. Thereby, the thesis shows the ways in which five key concepts - human rights, democracy, diversity, prosperity and security - are effective (‘their power’ or ‘efficacy’) and which Gestalt (‘meaning’) they take on in these specific problem-ridden situations. Particular attention is paid to the relationship and, specifically, tensions between the different normative concepts as well as the compromises that they form and the re-configuration of the respective policy fields they bring about. The thesis concludes that these findings should be interpreted as a self-understanding of the European Union. This self-understanding encompasses the commitment to a set of ideas, the decision to take action in certain political domains and, not least, the selfidentification as a political actor and entity. Thus, focusing on the power and Gestalt of concepts without falling into an abstract idealism, the thesis combines an approach of a historical sociology, cultural sociology and the history of concepts with key concerns of European Union studies.