Although declarations or predictions of a borderless world have become somewhat ubiquitous over the last twenty years, state borders remain one of the most basic and visible features of the international system. While it is true that a range of issues, like environmental change, migration, or international trade, highlight the growing interaction and interdependence between different places around the world, borders continue to play a central role in shaping, dividing, and uniting the world's societies, economies, and ecosystems. Reflecting their significance for scholars across the social sciences, a growing body of multidisciplinary research has investigated the continuing power of borders in our supposedly borderless world. This article examines some of the main lines of inquiry, research, and theory in this emerging field of border studies.