Ressentiment-the hateful desire for revenge-plays a pivotal role in Nietzsche's On the Genealogy of Morals. Ressentiment explains the formation of bad conscience, guilt, asceticism, and, most importantly, it motivates the "slave revolt" that gives rise to Western morality's values. This book brings it sharply into focus and provides the first detailed examination of Nietzsche's psychology of ressentiment. It shows how ressentiment, despite its blindness to justice, gives rise to moral justice-the central target of Nietzsche's critique. The result provides a novel view of Nietzsche's moral psychology in the Genealogy, his critique of morality, and his views on justice.