When we debate the US-Mexico border wall, we talk about its most obvious effect: the physical separation of people. But it turns out that there's another consequence that afflicts all those near a border, whether they're being entrapped by it or simply living near it: deleterious mental health effects. A growing body of research is proving that boundaries harm our brains. Foundational studies were done in the late nineteen-sixties on the effects of the Berlin Wall, uncovering cases of Berliners who were despondent, excitable, suicidal, paranoid, and more. Researchers gave the overarching condition a name: wall disease. Science journalist Jessica Wapner builds on this research, following the trail of psychological harm around the world--there are at least seventy border walls today, from the seventeen hundred miles of barbed wire walling off Bangladesh from India, to a five-layer fence stretches about six hundred miles between Saudi Arabia and Iraq, to the anti-immigration barriers between Bulgaria and Turkey, South Africa and Mozambique, Hungary and Croatia, and more. Weaving together interviews with those living up against walls with expert testimony from psychologists, economists, geographers, and other specialists who are publishing groundbreaking reports in outlets such as the Journal of Borderland Studies, she explores how borders affect the people who live near them in unforeseen ways. Whatever side of the political divide we fall on, we would do well to understand the inescapable toll of living up against a wall.