The goal of this dissertation is to explore how dual citizenship conceded by the Portuguese nationality legislation, overlapped with the European citizenship, allows the formation of new ideas of citizenship, dissolving boundaries of national participation and belonging. The confluence of nationality legislations of the member-states and the tolerance for dual citizenship, as characteristics of the European integration process, can only be understood in the social context in which interactions occur. Since the 1970s, migrations have raised questions about how states and the European integration process could and should deal with the challenges brought by diversity in a globalized world. After the consolidation of the Schengen area, the institutionalization process within the European Union has gone beyond the nation-state, creating a new logic of exclusion, in which a community of European citizens offers resistance to those who are not nationals, therefore to those who are (mostly illegal or non-qualified) immigrants. In fact, this logic reinforces and reconstructs traditional logics of exclusion, but because of its compromise with human rights, it also offers a new topic of discussion related to already existent immigrant communities. Accordingly, the Portuguese state has developed a dialectic relationship between, in one hand, its historical and cultural proximity with the Portuguese-speaking world and, in the other hand, the priorities of the European integration process. Since the 1980s it is possible to verify changes in the Portuguese nationality legislation and in its tolerance to dual citizenship. In this sense, those who obtain the Portuguese nationality - especially descendants of Portuguese immigrants born in former colonies - have the opportunity to participate in the exclusionary process of the European citizenship, at the same time pushing the communitary boundaries beyond the territorial limits of the Union.