This volume explores the consequences of past and ongoing processes of territorial rescaling on citizenship in a theoretical and comparative perspective. In this introduction, we unpack our core concept of territorial rescaling and discuss its implications for the citizenship status and rights of those groups and individuals who reside in the contested territory or are connected to it. We show that in the context of the European multilevel federation, territorial rescaling is rather the norm than the exception, an inherent feature of ongoing processes of integration and disintegration instead of an anomaly. The rescaling of territorial borders invariably leads to the realignment of membership boundaries. The articles focus on various related issues, such as the definition of the franchise in constitutive referendums; the democratic foundations of multilevel secession; and citizenship in ‘aspiring’ states, in ‘new’ states and in ‘contested’ states.