This chapter looks both the facts of the matter and the underlying theoretical issues. It is in the sense that immigration, and the borders that its control brings into play, reveal important and characteristic features of the contemporary state as such, and specifically underline the complexity, and in some respects the indeterminacy, of its territoriality. Perhaps one might reserve the phrase "migration" for forms of movement in physical space that are set within a broader class of "mobility" which may not involve physical movement at all. To be present in a territory is largely meaningless if one lacks the opportunity to work, access to some kind of housing, enjoyment of the basic social entitlements that define "full membership" in the Marshallian sense, and so on. In contemporary governance, jurisdiction is just one aspect, not necessarily even the most important, of the state.