The branch of philosophy concerned with the nature and extent of human knowledge is called epistemology (from the Greek epistēmē meaning knowledge, and logos meaning theory). Knowledge seems to come in many varieties: we know people, places and things; we know how to perform tasks; we know facts. Factual knowledge has been the central focus of epistemology. We can know a fact only if we have a true belief about it. However, since only some true beliefs are knowledge (consider, for example, a lucky guess), the central question asked by epistemologists is ‘What converts mere true belief into knowledge?’. There are many, and often conflicting, answers to this question. The primary traditional answer has been that our true beliefs must be based upon sufficiently good reasons in order to be certifiable as knowledge. Foundationalists have held that the structure of reasons is such that our reasons ultimately rest upon basic reasons that have no further reasons supporting them. Coherentists have argued that there are no foundational reasons. Rather, they argue that our beliefs are mutually supporting. In addition to the constraints upon the overall structure of reasons, epistemologists have proposed various general principles governing reasons. For example, it seems that if my reasons are adequate to affirm some fact, those reasons should be adequate to eliminate other incompatible hypotheses. This initially plausible principle appears to lead directly to some deep puzzles and, perhaps, even to scepticism. Indeed, many of the principles that seem initially plausible lead to various unexpected and unwelcome conclusions. Alternatives to the primary traditional answer to the central epistemic question have been developed, in part because of the supposed failures of traditional epistemology. These alternative views claim that it is something other than good reasons which distinguishes (mere) true beliefs from knowledge. Reliabilists claim that a true belief produced by a sufficiently reliable process is knowledge. Good reasoning is but one of the many ways in which beliefs can be reliably produced. The issue of whether the objections to traditional epistemology are valid or whether the proposed substitutes are better remains unresolved.