 The key idea behind Goldman’s reliabilist approach is that the justifiedness of a belief depends on the mental history of the subject’s belief. In particular, it depends on the reliability of the process(es) which cause the belief in question. Somewhat similar ideas (or segments thereof) have been advanced by a number of predecessors, often focusing on knowledge rather than justification. Frank Ramsey (1931) wrote that a belief qualifies as knowledge if it is true, certain, and obtained by a reliable process. He did not, however, provide a detailed defense of this thesis. Peter Unger (1968) proposed that S knows that p just in case “it is not at all accidental” that S is right about its being the case that p. David Armstrong (1973) offered an analysis of non-inferential knowledge that explicitly used the term “reliable”. He drew an analogy between a thermometer that reliably indicates the temperature and a belief that reliably indicates the truth. All of these writers seemed to endorse some variant of reliabilism, although typically there were minor or major differences from the version we shall focus on here. For example, Armstrong promoted an “indicator” variant of reliabilism rather than a “psychological process” variant. And Unger presented “non-accidentality” rather than “truth-conduciveness” as the central determinant of justifiedness. Clearly, however, there is a great deal of convergence in these views. So, contemporary defenders of epistemic reliabilism have grounds for optimism that they are laboring in promising terrain. The nitty-gritty details, however, still need additional work, as we shall see in the body of this entry. We turn now to some of the principal details of Goldman’s form of reliabilism for justification (Goldman, 1979, 1986).