While there is an enormous literature on friendship, next to nothing has been written about enemyship. This neglect may be due to the assumption that enemyship is simply inverted friendship. We reject that assumption and argue that although enemyship shares some important structural relations with friendship (such as dispositions to act and the presence of significant interactions), there are crucial differences. Unlike friendship, enemyship does not require reciprocity, mutual acknowledgment, or equality in any degree. If we are right, enemyship is a sui generis category of human relationship, in need of further exploration. To that end, we offer a conceptual analysis and taxonomy of enemies before turning to two normative questions: is there anything intrinsically good about having an enemy? Would a good person ever have enemies, of any kind?