This paper examines the social-psychological factors often implicated in discussions of terrorist violence/martyrdom, with a particular focus on the role of religion. We offer a brief description of the psychological theories underpinning terrorist research before focusing on social-psychological factors. The roles of psychopathology, irrationality and grievance/threat are examined, followed by empirical research on the beliefs which have been associated with the perpetration and support of terrorist violence, and the social factors which foster those beliefs, including social identity, socially carried interpretations, group leadership and individual differences. Although religion is not a single, simple causal factor in terrorist violence, religious elements often feature strongly in the belief systems associated with terrorist violence, and can also feature in other important fostering factors for terrorist violence, such as the use of rhetoric. Finally, the status of lay explanations of terrorist violence, focusing on the role of religious fundamentalism is examined.