When Janet Abu-Lughod sketched the contours of a medieval 'world system' in 1989, she located most communication networks in the southern hemisphere. In recent decades, however, new trends in research and new forms of evidence have complicated, enriched, and expanded this picture, geographically and chronologically. We now know that vast portions of the world were interconnected throughout the Middle Ages and, moreover, that the entire circumpolar North was a contact zone in its own right. In this volume, scholars from a range of disciplines explore the boreal globe from the late Iron Age to the seventeenth century, offering fresh perspectives that cross the frontiers of national historiographies and presenting new research on migration, trade, mapping, cultural exchange, and the interactions of humans with their environment.