A central argument of this article is that Isaiah Berlin's notion of cultural pluralism can be described as relativistic, and that he should not have repudiated the relativism, but simply defended it as part of the reality of the global constellation of cultures. Berlin's relativism emerges into a more generous light, in which radical differences among cultures occupy centre stage. Focusing on cultural relativism and its possible sources in Berlin unveils the neglected role that his famed concept of 'negative' liberty plays in assuring the distinctiveness of individual cultures and shared humanity, both of which constitute cultural pluralism. I conclude that Berlin's notion of cultural pluralism is relativistic based not only on substantive evidence, but also on a more realistic definition of the concept. Moreover, his conception of cultural pluralism and in particular its relativism highlight the subjects of cultural identity and autonomy in a world of immense power imbalances among nations and peoples.