Nationality and citizenship are frequently confused but analytically distinct concepts. In the context of the United Kingdom they are especially problematic, for state identity (British) and national identities (English, Scottish, Welsh, etc.) have evolved in a highly implicit manner since the state was formed in the eighteenth century. The development of multiculturalism in the second half of the twentieth century adds to this complexity and diversity. At the end of the twentieth century, nation, state and society are increasingly differentiated, presenting particular problems for sociology whose orthodoxies usually treat them as synonymous. Today, fewer societies can be described as ‘nation-states’. On the other hand, the United Kingdom is a multi-national and multi-cultural state in which ethnic and national identities sit uneasily alongside citizenship or state identity. Compared with modern republican states such as the United States or France, as well as Germany, the United Kingdom faces particular challenges to its historically implicit and complex set of political, territorial and ethnic identities.