Our world has innumerable boundaries. They range from the obvious—an ocean, or a mountain range—to subtle differences in language or climate. We cross boundaries all the time, sometimes without realizing it. They can be subjective: our perceptions of a boundary may not be shared by others. And yet they shape the way we engage with the world. Geographer Maxim Samson examines invisible lines, exploring the ways in which we divide this world—from meteorology and ecology to race and religion—and how they allow us to define “insiders” and “outsiders,” to identify places where particular attention and resources are especially urgent, to distinguish between two sides, two groups, two futures. From segregation along Detroit’s infamous 8 Mile to herds of red deer that still refuse to cross the former Iron Curtain, the existence—or perceived existence—of dividing lines has manifold implications for people, wildlife, and places. Vividly written and illustrated with maps, is a compelling exploration of boundaries in all their consistency, and all their messiness too.