If the consequences of identity fusion are well established, its psychological antecedents are not. To address this shortcoming, eight studies tested the hypothesis that self-verification (receiving evaluations that confirm one's self-views) increases fusion (a synergistic union with a group, individual, or cause), which, in turn, increases behavioral support for the target of fusion. Correlational studies showed that perceived self-verification was positively associated with fusion, which was positively associated with willingness to fight and die for a group (Study 1a), a value (Study 1b), and a leader (Study 1c). Study 2 revealed that increasing perceived self-verification fostered greater willingness to fight and die for the group but only indirectly through increases in fusion. Study 3 showed that 4 months after indicating the degree of fusion with a group, increasing perceived self-verification augmented endorsement of fighting and dying for the group indirectly through elevations in fusion. In Study 4, relational ties mediated the relationship between perceived self-verification and fusion. Finally, face-to-face interviews with incarcerated members of street gangs and organized crime gangs (Studies 5a-5b) showed that perceived self-verification was positively associated with fusion, which was positively associated with sacrifices for the gang (replicating Studies 1a-1c). No evidence emerged supporting a rival causal path in which fusion caused willingness to fight and die through perceived self-verification. Implications for related theoretical approaches and for conceptualizing the relationship between personal identities, social identities, and group processes are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).