The threat of terrorism and rise of extremist movements across the globe pose some of the greatest challenges the world currently faces. While there have been serious conceptual and methodological problems within the psychological study of terrorism, the nascent field has advanced and the evidence, theories, and models have developed in their sophistication. The current article explores the role of social or collective identity in instigating, propagating, and diminishing engagement in violent extremism. Specifically examining how when a fundamental need to belong is challenged through threats and uncertainty this can lead to the people joining entitative groups which can fuse personal and social identities. These identities can be further amplified through ingroup and outgroup processes leading to involvement in violent extremism. The paper also explores how identity can mediate the stress of this extremist lifestyle and sustain engagement in violence. In order to illustrate these processes the article draws on interviews with Northern Irish paramilitaries. Finally, the paper explores the role of identity in moderating violent extremism, and provides suggestions of approaches to promote desistence from violent extremism.