From a demographic point of view, naturalization represents an administrative and legal bridge between populations - both foreign and national. However, more than a change in the population distribution, changes of nationality also have a significance that goes beyond numbers; they impact the perception of the foreign presence on a given territory and, consequently, the narratives around that question. This element is crucial in a context such as Switzerland, where issues relating to foreigners and immigration are subject to intense media and political pressures. This is due, in particular, to the continuous growth of the proportion of foreigners since the 1980s, which reached a quarter of the resident population in 2021. Therefore, capturing and assessing the phenomenon of naturalization echoes questions of social cohesion, living together in harmony and, in some cases, social inequalities. In addition to its societal impact, naturalization also affects various aspects of people's lives, in terms of mobilities or economic, social and political integrations, and thus exerts a decisive influence on life trajectories.

Based on the particular case of Switzerland, this thesis enriches our understanding of the naturalization process and its various constituent stages. In addition to highlighting on contemporary trends and issues in Swiss ordinary and facilitated naturalizations, this manuscript also documents some disparities in access to a Swiss passport. Whether these disparities result from legal constraints or a personal will, they provide input for thoughts on Swiss policy and practices regarding the acquisition of nationality. In this context, we have identified some inclusion or exclusion factors characterizing the Swiss naturalization policy, as well as elements that encourage or discourage people from aspiring or initiating a procedure. Although results shed light primarily on the phenomenon of naturalization in the Swiss context, they also raise issues with a more general scope. Indeed, they contextualize the acquisition of a new nationality within a global hierarchical system, where citizenships do not necessarily come with the same rights and opportunities.

This manuscript gives an answer to the following questions: (1) In Switzerland, what issues have emerged from observing naturalization over the past 20 years? (2) What are the personal and contextual factors associated with the aspirations and practices of acquiring Swiss nationality? (3) How do these particular behaviors reflect structures for opportunities and obstacles that arise during or at the end of the naturalization process?