 The term “epistemology” comes from the Greek words “episteme” and “logos”. “Episteme” can be translated as “knowledge” or “understanding” or “acquaintance”, while “logos” can be translated as “account” or “argument” or “reason”. Just as each of these different translations captures some facet of the meaning of these Greek terms, so too does each translation capture a different facet of epistemology itself. Although the term “epistemology” is no more than a couple of centuries old, the field of epistemology is at least as old as any in   philosophy.[1]   In different parts of its extensive history, different facets of epistemology have attracted attention.  Plato’s epistemology was an attempt to understand what it was to know, and how knowledge (unlike mere true opinion) is good for the knower. Locke’s epistemology was an attempt to understand the operations of human understanding, Kant’s epistemology was an attempt to understand the conditions of the possibility of human understanding, and Russell’s epistemology was an attempt to understand how modern science could be justified by appeal to sensory experience. Much recent work in formal epistemology is an attempt to understand how our degrees of confidence are rationally constrained by our evidence, and much recent work in feminist epistemology is an attempt to understand the ways in which interests affect our evidence, and affect our rational constraints more generally. In all these cases, epistemology seeks to understand one or another kind of cognitive success (or, correspondingly, cognitive failure). This entry surveys the varieties of cognitive success, and some recent efforts to understand some of those varieties.