Terrorism, whether it is group-related or performed as lone actor terrorism, is a predominantly male phenomenon. Generally and throughout history, young males have been the main protagonists of criminal and political violence.This article aims to contribute, from different perspecives, to the question of what makes young men violent. These include neurobiological aspects, such as sex differences in the brain that predispose males to physical aggression and violence; gender role aspects, with regard to aggression and violence being basic components for demonstrating and reconstructing masculinity; demographic aspects of male youth bulges as potential breeding grounds for terrorism; aspects of group dynamics and identity fusion in the process of radicalization; and psychosocial characteristics of lone actor terrorists, which differ from group-related terrorists.It is concluded that in addition to ideological, political, economic, regional, demographic, or psychosocial causes, experiences of threatened masculinity may be an underlying factor and driving force for terrorism.