Using an intergroup version of the trolley problem, we explored participants' willingness to sacrifice their lives for their group. In Study 1, Spaniards whose personal identities were fused with their group identity endorsed saving fellow Spaniards by jumping to their deaths in front of a runaway trolley. Studies 2 and 3 showed that the self-sacrificial behaviors of fused Spaniards generalized to saving members of an extended in-group (Europeans) but not members of an out-group (Americans). In Study 4, fused participants endorsed pushing aside a fellow Spaniard who was poised to jump to his death and initiate a chain of events that would lead to the deaths of several terrorists, so that they could commit this act themselves. In all four studies, nonfused participants expressed reluctance to sacrifice themselves, and identification with the group predicted nothing. The nature of identity fusion and its relationship to related constructs are discussed.