This short book outlines the case for border abolition as the only viable response to the nightmarish realities of our present. It develops a thoroughgoing critique of contemporary border regimes, while identifying critical openings for alternative futures. Ours is the age of borders and walls. The government of mobility has become the central problem of the 21st century, as states develop new and terrifying ways to fix and manage unequal populations in space and in law. The violence of borders is everywhere visible: in the brutality of the UK’s hostile environment, clarified in chilling detail by the Windrush scandal; in the so-called refugee crisis at Europe’s borders; and in the violent caging and separation of migrant children and families in the U.S. Today’s borders and walls are both cause and effect of the converging constellation of fascist movements across Europe, the U.S. and Australia, in which we see the cultural and political re-mainstreaming of overt forms of racism and white supremacy. In response to both left nationalisms and liberal campaigns for nicer immigration regimes, Against Borders argues for border abolition, building on black feminist writing and activism on prison abolition. Working towards a world without borders is not simply about unmaking the institutions of immigration control. We need new ways of living together and relating to one another, far from the racialised, nationalised and territorialised identities that structure contemporary political imaginaries.