This thesis asks what kind of conception(s) of citizenship that have emerged over time within the European integration process. The starting point for this research aim is a critique of the existing literature on European citizenship. Research on European citizenship has tended to fall into a sceptical strand relying on the nation-state model of citizenship (often called the no demos position) or a more visionary strand which interprets the developments of rights on the EU level as a postnational disconnection of citizenship from nationality. These normative strands have tended to translate the question of 'what should it be?' into factual statements on what citizenship in the EU actually is. This thesis has sought to overcome this through a theoretically informed, yet empirically oriented study of how conceptions of European citizenship have developed. Theoretically, the thesis eschews the typical model approach of citizenship studies. It does so by focusing on citizenship as a status of individuals constituted through four analytically distinct, yet potentially inter-related dimensions: membership, rights, participation and identity. This provides a dynamic theory of citizenship where the appearance of and relationship between dimensions is not settled a priori, but rather needs to be scrutinised in practice. Empirically, therefore, these dimensions are utilised in order to ascertain how citizenship has been conceived on two levels of EU integrative politics. The first level is practices of policy- and law-making, starting with the founding treaties of the 1950s and ending with the post-Maastricht debates on Union citizenship. The second level is three instances of constitution-making importance within European integration: the Spinelli Project of the European Parliament, the Maastricht Process and the Convention on the Future of Europe. Methodologically, the analytical assessment of European citizenship discourse is provided on the basis of a process tracing exercise geared towards highlighting the crucial junctures of appearance, consolidation, and/or change with regard to the concept of citizenship. The main conclusion is that European citizenship discourse has created a conception of transnational citizenship, rather than postnational membership. This is visible on both empirical levels. The inherent transnationalism of European citizenship is found to have been initiated already in the founding ECSC and Rome Treaties. Citizenship elements in early European integration, such as free movement, market participation and, later, membership based on nationality in a Member State, created a frame upon which ensuing conceptions of citizenship developed. There were proposals for alternative conceptions based on a stronger notion of a more free-standing European status, for instance in elections to the EP, and more radical ideas of membership through dual European and national citizenship within constitution-making instances. Such proposals did, however, not significantly alter the conception of European citizenship as articulated around the border-crossing of Member State citizens. As much as this has highlighted - against the no demos view - that issues of citizenship are not incompatible with institution building and policy-making 'beyond the nation-state', it is also clear that one cannot detect a significant dissociation of citizenship and rights from nationality, as professed by postnationalists. Citizenship has evolved - mainly within policy practices - as a significant status of individuals within European integration through a transnational 'right to have rights' in second countries. Constitution-making instances have on the whole contributed to a consolidation of the basic tenets emanating from policy practices, rather than producing radical 'constitutional moments' of EU citizenship politics. The conceptual path of European citizenship discourse has, therefore, brought forward a conception based on a core principle of 'no rights without movement'; where elements such as political rights on the European and Member State levels, personhood as an additional condition for access to rights, and residence rights have been added as a consequence of evolving policies and practices of European integration.