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Although cooperation between groups is not unusual, most forms of human cooperation are in-group bounded and, sometimes, motivated by the desire to ward-off and subordinate rivaling out-groups. Building on evolutionary perspectives and models, we propose that humans evolved a capacity for parochial cooperation, which entails (1) in-group love: the tendency to cooperate with and extend trust toward those others who are similar, familiar rather than unfamiliar, and belong to one's own group; and (2) out-group hate: a willingness to fight against rivaling out-groups. This chapter reviews our own work, and that of others, showing that parochial cooperation (1) emerges especially when it benefits individuals' within-group reputation, (2) affects one's within-group status, (3) is more prominent among individuals with chronic prosocial rather than proself value orientation, and (4) is sustained and motivated by …