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. So whether a true belief is knowledge is not merely a matter of supporting beliefs or reliability; in the case of knowledge, practical rationality and theoretical rationality are intertwined. Stanley defends this thesis against alternative accounts of the phenomena that motivate it, such as the claim that knowledge attributions are linguistically context-sensitive (contextualism about knowledge attributions), and the claim that the truth of a knowledge claim is somehow relative to the person making the claim (relativism about knowledge). In the course of his argument 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.