The dissertation examines one of the most remarkable and controversial developments in the recent history of European integration, namely the institutionalization of a regional policy regime to manage the continent's frontiers. By adopting this regime (known in policy circles as ‗Schengen'), European governments have in fact relinquished part of their sovereign authority over the politically sensitive issue of border control, thereby challenging what for a long time was the dominant national approach to policy-making in this domain. In order to account for the regime's emergence and success, a constructivist analytical framework centred on the notion of ‗cultures of border control' is advanced. From this perspective, the adoption of a regional approach to govern Europe's frontiers is the result of the evolution of a nationalist (‗Westphalian') culture-or set of background assumptions and related practices about borders shared by a given policy community-into a post-nationalist one (‗Schengen'). The cultural Channel. This rhetorical move seemed well founded. Indeed, it was in continental Europe that the modern ‗national' conception of borders first emerged (Anderson 1996). According to this conception (which has its roots in the early phases of the modern state-system in 17 th century Europe), borders are continuous territorial lines marking the outer limits of a state's authority and a key foundation around which the principle of sovereignty in the international system is built. Borders represent the very essence of statehood (delimiting its authority in the international system) and one of its most visible embodiments (its ‗skin', according to an oft used biological metaphor). At the same time, borders are a powerful symbol of identity and historical continuity, both for the state as institution and for the peoples they contain. Their protection is therefore a matter of ‗national security', and the exclusive responsibility of central governments. This perspective has long imbued official arguments and practices in the border control domain in Europe (and elsewhere), and it has been widely accepted by both decision-makers and the population at large. Thatcher's take on border control should have resonated well with a European audience. But it didn't. On the contrary, while she was delivering her speech, something extraordinary was under way in the heart of Europe. Since the mid-1980s, a group of European countries (France, Germany, the Benelux) had been taking the first steps towards the abolition of controls over their shared frontiers. The goal of the emerging border control regime (which would be known as ‗Schengen', from the name of the Luxembourg town where the founding agreement was originally signed) was the creation of a common space where, not only goods and capital, but also individuals would be free to circulate. Schengen did not imply that borders were to completely disappear or lose importance. In order to compensate for the perceived security deficit stemming from the elimination of controls at comm...