This unique book represents one of the first systematic attempts to explain why thousands of Westerners heed international calls to _jihad_ and join radical Islamic groups. Drawing on his unprecedented access to a radical Islamic group, Quintan Wiktorowicz details the subtle process that can turn seemingly unreligious people into supporters of religious violence. The author's extraordinary fieldwork forms the basis of a detailed case study of alMuhajiroun, a transnational movement based in London that supports Bin Laden and other Islamic terrorists. Through its rich empirical detail, the case study explains the larger question of why ordinary people join extremist movements.