This chapter analyses in detail how, and by whom, EU citizenship has been conceptualised and shaped in order to discuss and answer three crucial questions. First question is how can a conceptual innovation, such as Union Citizenship, be filled with meaning and also with a new institutional practice. Second, which conflicts, actors and strategies are decisive in these processes. And third, which particular shape does the concept of citizenship take on in the EU, and which new questions does this new shape give rise to. The chapter discusses the particularities of these processes with regard to the crucial concepts of non-discrimination and free movement of persons that have a central role in the development of EU citizenship. It compares the development of EU citizenship practice to the modes of shaping citizenship in Western nation states during their democratisation period, and then discusses consequences of these differences for citizenship as a concept more generally.