With novel conceptual discussions and probing fieldwork, Apart explores why many Western Muslims are disaffected, why others are engaged, and why some seek to undermine the very political system that remains their primary means of inclusion. Based on research conducted in London's East End and Madrid's Lavapies district, and drawing on over 100 interviews with community elders, imams, extremists, politicians, gangsters, and ordinary people just trying to get by, Justin Gest reveals young Muslim men s daily existences. Confronting conventional explanations that point to inequality, discrimination and religion, he builds a new theory arguing that alienated and engaged political behavior is distinguished not by structural factors, but by how social agents interpret their shared realities. Filled with counterintuitive conclusions, Apart sounds an unambiguous warning to Western policy-makers, and presages an imminent American experience with the same challenges. How both governments and people discipline their fear and understand their Muslim fellows may shape democratic social life in the foreseeable future.