This book maps out, from a variety of theoretical standpoints, the challenges generated by European integration and EU citizenship for community membership, belonging and polity-making beyond the state. It does so by focusing on three main issues of relevance for how EU citizenship has developed and its capacity to challenge state sovereignty and authority as the main loci of creating and delivering rights and protection. First, it looks at the relationship between citizenship of the Union and European identity and assesses how immigration and access to nationality in the Member States impact on the development of a common European identity. Secondly, it discusses how the idea of solidarity interacts with the boundaries of EU citizenship as constructed by the entitlement and capacity of mobile citizens to enjoy equality and social rights as EU citizens. Thirdly, the book engages with issues of EU citizenship and equality as the building blocks of the EU project. By engaging with these themes, this volume provides a topical and comprehensive account of the present and future development of Union citizenship and studies the collisions between the realisation of its constructive potential and Member State autonomy.