The book develops a normative theory of criminal disenfranchisement and determines which offenders may justifiably lose electoral rights after criminal conviction. Having examined the historical development of the practice and contemporary electoral restrictions—which reveal that disenfranchisement is still widespread in European democracies—the book goes on to explore the nature of this sanction and its normative foundations. Diverging from common understanding, the book proposes that criminal disenfranchisement is not a form of punishment, but a citizenship sanction that aims to reduce membership entitlements of disenfranchised criminals and deplete their citizenship status. To determine whether criminal disenfranchisement can be justified, it is necessary to understand the substance of membership in a polity and the requirements that a citizen ought to satisfy to enjoy a full range of rights attached to this status. To account for possible differences in citizenship requirements between diverse types of polities, the book develops three ideal-typical models, which are loosely tied to the liberal, republican, and communitarian forms of political organization. The book contends that, regardless of internal differences, only one kind of criminal offender fails to satisfy citizenship requirements in all three types of polity and may thus incur electoral restrictions—a person who has seriously and irreversibly severed citizenship ties with her polity owing to an incorrigible lack of moral conscience. The book concludes by specifying additional conditions that ought to be satisfied before restrictions can be enacted, but also suggests reasons for which polities may abstain from imposing them.