This paper considers the significance of citizenship in all aspects of penal law (substantive criminal law, criminal procedure, punishment execution), with particular attention to the so-called War on Terror. It concludes that the concept of citizenship can play a useful, though not necessarily a central, role in a descriptive account of penal practice. By contrast, it contributes nothing to a normative theory of criminal law, being either empty, as a proxy for personhood, or pernicious, as a proxy for insiderhood.