Thisarticlefocusesonthepoliticalclaimsmadebyimmigrantsandethnicminori- ties in France and Switzerland. We look at cross-national variations in the overall presence of immigrants and ethnic minorities in the national public space, and the forms and content of their claims. Following a political opportunity approach, we argue that claim-making is affected both by institutional opportunities and by national models of citizenship. The civic- assimilationist conception of citizenship in France gives migrants greater legitimacy to intervene in the national public space. Furthermore, the inclusive definition of ‘membership in the national community' favors claims pertaining to minority integration politics. However, the pressure toward assimilation to the republican norms and values tends to provoke claims for the recognition of ethnic and cultural difference. Finally, closed institutional opportunities push migrants' mobilization to become more radical, but at the same time the more inclusive model of citizenship favors a moderate action repertoire of migrants. Conversely, the ethnic-assimilationist view in Switzerland leads migrants to stress homeland-related claims. When they do address the policy field of ethnic relations, immigration and citizen- ship, they focus on issues pertaining to the entry and stay in the host society. Finally, the forms of action are more moderate due to the more open institutional context, but at the same time the action repertoire of migrants is moderated by the more exclusive model of citizenship. Our article is an attempt to specify the concept of ‘political opportunity structure', and to combine institutional and cultural factors in explaining claim-making by immi- grants and ethnic minorities. We confront our arguments with data from a comparative project on the mobilization on ethnic relations, citizenship and immigration.