In recent times, the phenomenon of lone wolf terrorism has been observed with the social assumption that a radicalized individual is only guided by personal, social, and ethnic reasons to commit an extremist act. Nevertheless, there is still much to understand about this phenomenon and improve the methods of investigation or psychiatric interventions. This handbook attempts to cover gaps in understanding the psychiatric aspects of radicalization and the phenomenon of lone-wolf terrorism. Edited by expert clinical psychologists, the contributors have taken both a qualitative and theoretical route to analyze the phenomenon, prompted by their clinical experience with mental health professionals, being in contact with radicalized people living in local towns and prisons.