Jason Stanley presents a startling and provocative claim about knowledge: that whether or not someone knows a proposition at a given time is in part determined by his or her practical interests, i.e. by how much is at stake for that person at that time. In defending this thesis, Stanley introduces readers to a number of strategies for resolving philosophical paradox, making the book essential not just for specialists in epistemology but for all philosophers interested in philosophical methodology. Since a number of his strategies appeal to linguistic evidence, it will be of great interest to linguists as well.