Delegitimization is the process of categorizing groups into extremely negative social categories and excluding them from acceptability. This paper analyzes the causes and consequences of delegitimization, and suggests two models that describe the role of conflict in delegitimization and of ethnocentrism in delegitimization. During conflict, when the ingroup perceives the negating goal(s) of an outgroup as far-reaching and evil, feelings of threat become intensified and delegitimization may be used to explain the conflict. Then, to prevent danger, the ingroup may harm the threatening group and justify the harm by delegitimization, which in turn increases perceived threat and intensifies harmful behavior toward the other group. Even mild conflicts can escalate, become violent, and lead to delegitimization as an explanation, and later, as justification. Ethnocentrism is related to this process because groups that are perceived as very different and devalued arouse feelings of fear and contempt. Their delegitimization leads to harm, and later, to intensified delegitimization to justify the harm.