Citizenship legislations of the Member States of the European Union are the result of common principles, shared influences and various constitutional identities. Altogether, they revolve around a set of international rules and converge on a general status: European citizenship. Building on this tension between unity and diversity, this report aims to describe the rules regarding loss of citizenship within the Member States (adding the United Kingdom), compare legislations and analyse both recent trends and ancient origins from a legal perspective. The six main categories that this report follows in order to examine citizenship loss in the European Union are divided between voluntary (renunciation) and involuntary loss of citizenship (possession of another nationality; residence abroad; disloyalty or lack of merit; fraud and similar acts; loss linked to family relationship).