This is the first book devoted to the work of Ernest Sosa, one of the most influential contemporary epistemologists. It is part of the acclaimed "Philosophers and Their Critics" series. The editor's introduction serves as an introduction to Sosa's epistemology. This work contains critical essays by more than twenty of the most prominent epistemologists in the world, commenting on Sosa's work. It concludes with Sosa's own reply to his critics.