Cultural relativism continues to be closely identified with anthropology even though few anthropologists today endorse the comprehensive version of it first articulated by students of Franz Boas. A review of the progressive reduction of the scope of cultural relativism since the early decades of the twentieth century suggests that it should be regarded not as a comprehensive theory or doctrine but as a rule of thumb that when used prudently serves the limited but indispensable function of keeping anthropology attentive to perspectives that challenge received truth.