In epistemology and in philosophy of language there is fierce debate about the role of context in knowledge, understanding, and meaning. Many contemporary epistemologists take seriously the thesis that epistemic vocabulary is context-sensitive. This thesis is of course a semantic claim, so it has brought epistemologists into contact with work on context in semantics by philosophers of language. This volume brings together the debates, in a set of twelve specially written essays representing the latest work by leading figures in the two fields. All future work on contextualism will start here. Contributors: Kent Bach, Herman Cappelen, Andy Egan, Michael Glanzberg, John Hawthorne, Ernest Lepore, Peter Ludlow, Peter Pagin, Georg Peter, Paul M. Pietroski, Gerhard Preyer, Jonathan Schaffer, Jason Stanley, Brian Weatherson, Timothy Williamson