The Habsburg-dominated southeastern Europe has been, since the eighteenth century, a space of military expansion, political (re)ordering, and increasing cultural interconnectedness. Imperial, national, and later transnational spatial concepts often existed here not linearly, but in competition with one another, overlapping and interacting. This volume traces these spatial notions from a longue durée perspective, focusing on border zones, transitions, and processes of exchange. The contributions cover topics ranging from military and administrative spatial thinking to cultural networks, reform ideas, and utopian designs, as well as the long-term effects of the Habsburg monarchy’s collapse after 1918 in the successor states. At the same time, they connect these historical developments to the present, where questions of European cooperation, borders, and belonging have once again gained urgency. The volume understands southeastern Europe not as a peripheral zone, but as a historical space of European experience.