Master–slave morality (German: Herren- und Sklavenmoral) is a central theme of Friedrich Nietzsche's works, particularly in the first essay of his book On the Genealogy of Morality. Nietzsche argues that there are two fundamental types of morality: "master morality" and "slave morality". Master morality values pride, wealth, fame and power, while slave morality values kindness, empathy, and sympathy. Master morality judges actions as good or bad (e.g. the classical virtues of the noble man versus the vices of the rabble), unlike slave morality, which judges by a scale of good or evil intentions (e. g. Christian virtues and vices, Kantian deontology).

For Nietzsche, a morality is inseparable from the culture that values it, meaning that each culture's language, codes, practices, narratives, and institutions are informed by the struggle between these two moral structures.