Résumé : This dissertation focuses on the issue of registration of foreign residents (EU and non-EU) for the 2012 local elections in Belgium. The goal of this study is twofold. First, it aims at identifying and analyzing the factors explaining variations in foreigners’ registration between municipalities. The second objective is to understand how and why these explanatory factors have an impact on their decision to register. A mixed-methods approach is used to provide a broad and comprehensive picture of the registration of foreign citizens. It is assumed that foreigners’ registration rates for municipal elections vary according to the formal and discursive political opportunities at the local level. I also argue that the political opportunities approach needs to be combined with other predictors that are specific to migrant groups. The quantitative results indicate that the presence of a left-wing mayor in the municipality displays a strong positive and significant association with both EU and non-EU registration. Moreover, the results provide a strong support for the hypothesis relating to outreach actions: municipalities organizing many foreign voter outreach actions are more likely to achieve high foreigners’ registration rates than municipalities that organize no action or only a limited number. In addition, the findings show that foreigners’ registration does not depend only on political opportunities, but also on specific characteristics of foreigners relating to their migration process. First, the residential instability has a negative impact on both EU and non-EU registration. Second, municipalities with a high percentage of non-EU residents with the nationality of a country where one of the languages spoken is French or Dutch are slightly more likely to achieve high registration of non-EU nationals. It has been shown that political context matters for foreigners’ registration, but several questions emerge about the way it does matter. Based on the statistical results, three typical and three deviant municipalities were selected to disentangle the causal mechanisms between the presence of a left-wing mayor and foreigners’ registration on the one hand, and between the organization of outreach actions and foreigners’ registration on the other hand. The qualitative part of this study examines the theoretically widely supported, but empirically understudied assumption that citizens perceive opportunities in their socio-political context, and that their perception influence whether or not they will register on electoral lists. It emphasizes the interactions between actors and the political context and it takes into account causal mechanisms that link macro-level political opportunities and micro-level electoral participation. The case studies demonstrate that the decision to register does not always depend directly on perceived favorable political context but that more subtle and indirect elements such as the perception of the municipal climate as welcoming and the feeling of integration, influence greatly registration and should therefore receive more attention.