The contemporary political sphere is characterized by an increase in the number of regulation levels. A new structure has been emerging, defined by the overlay of national institutions, sub-state entities and supranational regional and international) organizations. The State, while remaining in a privileged position, no longer monopolizes the production of policiesï¼› the national area is not the sole locus of political life anymore. Such dynamics of change have affected the design of citizenship, central element of politics. The 1990s have seen a proliferation of studies regarding post/trans/supra-national, or global, citizenshipï¼› according to those analyses, the locus of citizenship is less and less national and more and more supranational. From a multiple and dynamic understanding of citizenship, the dissertation proposes to move beyond the locus issue. Citizenship is here conceived as a dynamic construction, whose moving outlines evolve through time and space. Individuals are not citizens “by nature”ï¼› they become citizens through a “citizenization” process, as political entities are built and consolidate. Institutional structures and public policies set up within supranational political entities create citizenship links with individuals, and those links evolve as institutional structures and policies are changing. The dissertation presents a contextualized analysis of the “citizenization” processes in progress at the supranational level. In this regards, it questions the meaning of the recent developments that affected the European Union and the United Nations for supranational citizenship-building. Important pillars of the multilevel governing structure characterizing the current political sphere, both entities have been engaged for the last years in profound institutional reform processes. Relying notably on the concepts of “citizenship regime” and “governance” and an institutionalist theoretical framework, the dissertation proposes an analysis of the impact of the institutional changes in progress within the European Union and the United Nations in citizenization terms. Keywords: Citizenization – European Union – United Nations – Citizenship regime – Governance – European citizenship – Active citizenship – Participation – Institution-building – Institutionalism.