We introduce a model of group threat that articulates the opposing effects of intergroup (between-groups) and intragroup (within-group) threat on identity processes and group relations. The source model of group threat argues that the perceived source of a threat is critical in predicting its consequences, such that perceptions of intergroup threat will strengthen (in)group identity processes and relations, whereas perceptions of intragroup threat has the potential to undermine the same. In addition to reviewing the large literature on intergroup threat and a smaller body of unsynthesized work on intragroup threat, we discuss how these processes are captured in representations of monsters (aliens, vampires, and zombies) in popular media and how these ideas can inform interpretation of current political debates, such as those around homegrown terrorism. This model provides a novel summary of the core effects of intergroup and intragroup threat, generating testable hypotheses about the psychological effects of different types of threat. Applying this model will help to make sense of seemingly contradictory findings in the literature, illustrating how appraisal of a threat as originating from an intergroup or intragroup source has the capacity to change the group-based effects of that threat. (PsycINFO Database Record (c) 2019 APA, all rights reserved).