Cultural relativism is the idea that a person's beliefs and practices should be understood based on that person's own culture. Proponents of cultural relativism also tend to argue that the norms and values of one culture should not be evaluated using the norms and values of another.

It was established as axiomatic in anthropological research by Franz Boas in the first few decades of the 20th century and later popularized by his students. Boas first articulated the idea in 1887: "civilization is not something absolute, but ... is relative, and ... our ideas and conceptions are true only so far as our civilization goes". However, Boas did not coin the term.

The first use of the term recorded in the Oxford English Dictionary was by philosopher and social theorist Alain Locke in 1924 to describe Robert Lowie's "extreme cultural relativism", found in the latter's 1917 book Culture and Ethnology. The term became common among anthropologists after Boas' death in 1942, to express their synthesis of a number of ideas he had developed. Boas believed that the sweep of cultures, to be found in connection with any subspecies, is so vast and pervasive that there cannot be a relationship between culture and race. Cultural relativism involves specific epistemological and methodological claims. Whether or not these claims necessitate a specific ethical stance is a matter of debate. The popularization of cultural relativism after World War II was somehow a reaction to such historical events as Nazism, and to colonialism, ethnocentrism and racism more generally.