Citizenship has emerged only recently as an important topic of research on migration and migrant integration. Before the late 1980s there was little connection between migration research and the legal literature on nationality laws or political theories and sociological analyses of citizenship in a broader sense. In traditional overseas countries of immigration immigrants’ access to citizenship and eventual naturalisation was taken for granted as a step in a broader process of assimilation, while in Europe the largest immigration contingents had emerged from the recruitment of guest workers who had been invited to stay only temporarily and were never perceived as future citizens.

Both expectations were eventually undermined when the dynamics of the migration process interacted with political developments to generate more inclusive conceptions of citizenship. Family reunification turned guest workers into settled immigrants. Many among these, however, maintained strong ties to their countries of origin. For these migrants, retaining the nationality of origin was a natural choice both for its instrumental value as a bundle of rights and for its symbolic value as a marker of ethno-national identity. At the same time, the rights of permanent residents in major democratic receiving states were upgraded in many areas or even equalised with those of citizens. Finally, more and more countries of immigration abandoned the consensus in international law that those who naturalise have to renounce their previous nationality and a growing number of sending countries also accepted multiple nationality among their expatriates. All these developments have blurred the previously bright line separating aliens from citizens. While some observers welcomed these trends as heralding a new cosmopolitan era in which state-bound citizenship would eventually be overcome, others were concerned about migrants’ multiple loyalties, their apparent free ride on citizenship rights without corresponding duties and about the political mobilisation of ethnic or religious identities.

Three core concepts

In this chapter we trace the main steps in these developments and highlight areas of agreement and controversy among researchers. We have identified three analytical concepts that provide common reference points for our analyses.

The first among these concepts is a society's political opportunity structure. This concept has been widely used in research on migrants’ political behaviour and activities, including voter turnout and representation in political bodies, membership in political parties and organisations, lobbying, public claims-making and protest movements.