Citizenship is a source of (legal) identity that provides access to resources, rights, and recognition. However, the contested nature of aspirant states leads to their citizens being subject to multiple (conflicting) citizenship regimes. This thesis sheds light on the complex relationship between contested statehood, citizenship regimes, and the politics of belonging. Using the lenses of multiplicity and human/state security, the thesis explores and explains how the phenomenon of citizenship has been constructed in three aspirant states in the former Soviet space: Abkhazia, South Ossetia, and Transnistria. The study employs a comparative case design approach and uses legislation, interviews, and survey data to understand citizenship from the perspective of law, administrative practices, and lived experiences. Furthermore, only by looking at the phenomenon from both the state and individual levels is it possible to explain the legal and socio-political implications of overlapping citizenship regimes. The thesis finds that the contested nature of aspirant states requires their citizens to navigate between the citizenship regimes of the aspirant, patron, base, and third states. Experiences of citizenship change depending on physical location, determinations by different states as to what legal status(es) an individual holds, and legislative and political changes. While legal status, rights, and identity are often interconnected, multiplicity of legal statuses does not always translate to a multiplicity of rights or identities. Further, citizenship regimes and constellations can become hierarchical due to their diverse levels of functionality. Meanwhile, from the state level, citizenship is used as a state- and nation-building tool to enhance ethno-demographic security by excluding undesired groups and including desired ones. Lastly, the thesis emphasises the normalisation discourse among (citizens of) aspirant states regarding their citizenship and security. This discourse evidences a broader pattern among aspirant states, highlighting that their state- and nation-building projects are not so different from recognised states. The main contribution of this thesis lies in expanding theoretical and empirical knowledge on citizenship in aspirant states and challenging the dominant practice of adopting IR, legal, and political science approaches and studying contested territories from the state level. Only by keeping the individual at the centre of study is it possible to understand and address human rights and human security issues they face.