Contemporary philosophers can be classified in terms of the other—non-philosophical—fields of inquiry that most impact on their respective philosophical work. For present-day epistemologists and philosophers of science the most influential fields are cognitive science, evolutionary biology, neuroscience, and physics. I belong to the small minority that believes that some of the most important challenges to philosophy today come from the sociology of knowledge. In this programmatic essay 1 sketch how epistemology must change if it wishes to do justice to what is valuable and lasting in the sociologists' insistence that knowledge is a social institution. This essay is not, however, an introduction to the sociology of knowledge. I seek to bring out the fundamentally social nature of knowledge through a discussion of philosophical theories. My aim is to arrive at, or recapture, some of the sociologists' insights by discussing philosophical texts and arguments.