This work examines the rules of citizenship in the 15 member states of the European Union, discussing their interpretation and enforcement, and the issues which arise within domestic and international law, taking a country-by-country approach to this subject. Each chapter written in English or French, provides an analysis of the various national provisions and regulations, with commentary on their construction and evolution, jurisprudence and citizenship procedures. It addresses the following issues: acquisition and loss of citizenship; consequences of filiation and marriage; the phenomenon of dual or multi-nationality; and the determination of the status civtatis, especially concerning the conflict and jurisdiction of rules, and the recognition of rights and duties.