It is notoriously diffi cult to defi ne the region. It is a territorial space, certainly, so we can exclude virtual spaces from our consideration, but it can take a number of territorial confi gurations. There is a conventional but still useful distinction between substate regionalism, studied traditionally by geographers, planners, sociologists, political scientists and historians, and supra-state regions, studied by other geographers and in international relations and strategic studies. Economists may make use of both. A third conception is the transnational region, which cuts across the boundaries of states, taking in some but not all of the territory or more than one political community. All these meanings, however, are relative to the nation-state, being above, below, or across it but not questioning its standing as the authoritative defi ner of territorial boundaries. Most of them also unproblematically use the term “nation-state” to defi ne both a sovereign polity and one in which state and nation coincide, although in plurinational polities these are quite diff erent meanings.