This paper starts from the concept of identity to develop some hypotheses about the attitudes of people toward national identity and citizenship. It is proposed that there are two factors which determine these attitudes: an evaluative-normative component related to the symbolic value of citizenship and a strategic orientation which considers the advantages connected with a particular passport. Empirical findings from the International Social Survey Program (ISSP) on National Identity and Citizenship are presented. It is shown that citizenship is a very important component of national identity in the eyes of the public and migrants usually exhibit a dual identity toward their countries of origin and destination. The surprisingly low naturalisation rates among immigrants in Western societies are also explained by two general factors: people do not want to lose their original national attachments; however, they also consider the instrumental advantages from acquiring the citizenship of the new country. Two further issues are discussed: the need for well-functioning democracies to have active citizens and the obligations connected with citizenship – of which these three are the most relevant: taking part in voting, paying taxes and, for men, performing military service. In the concluding section, the chapter points to the need to facilitate naturalisation, extend options of dual citizenship and improve the situation of denizens. Citizenship is a topic investigated mainly by scholars of public law and political scientists (Bauböck 1994; Hammar 1990; Spiro 2016). A number of sociologists have also contributed to this discussion (Brubaker 1992, 2010; Joppke 2010; Soysal 1994). In fact, sociology can contribute not only to the social aspects of citizenship but also to the discussion of the emergence and social impact of legal principles. At least since the writings of the Austrian legal scholar Eugen Ehrlich (1862–1922), we know that the legal reality of a community cannot be captured by looking only at formal written law because it also includes local and regional norms and customs and has a cultural and political character (Cotterell 1992; Ehrlich 1989 [1913]; Rehbinder 2014). In this chapter, I discuss three issues: first, the relevance of citizenship for personal, social and political identity in the modern world; second, some empirical data on the relevance and meaning of citizenship, as people in about 40 countries from all continents see it; and, third, three additional aspects of citizenship relevant from a sociological perspective. In the conclusions, the findings are summarised and some normative conclusions drawn concerning the policies of naturalisation and the issue of dual citizenship.