The present Companion, like the majority ofthe other volumes in the Blackwell Companionsto Philosophy series, is organized as astandard reference book, with alphabeticallyarranged articles of varying length (anythingfrom 250 to 3500 words) on leading theories,thinkers, ideas, distinctions and concepts inepistemology. It aims for a broad readership,while recognizing that the nature of contemporaryepistemology inevitably imposes restrictionson this. In some other areas of philosophyit remains feasible to design a book which islargely accessible to the general reader; inepistemology, however, the main readershipis likely to be students from undergraduate levelupwards, as well as professional philosophers,and it is to them that the Companion is primarilyaddressed.