The epistemology or theory of knowledge is a discipline that, already cultivated by the classical Greek philosophers and consolidated by the work of the moderns, occupies a central place in all current currents of philosophy. Its scope is not reduced to a mere compilation of the concepts that appear in the developments of other disciplines (logic, psychology, linguistics, artificial intelligence, etc.), and even less to the simple reconstruction of the "epistemological" contributions? of them incidental? of the great authors of the past, but it is the result of the confrontation of their specific ideas (experience, truth, conscience, intelligence, reason, belief, knowledge, etc.) with those of other scientific and technological fields (cognitive science, engineering of knowledge, etc.) in which epistemology has a fundamental influence today. At the same time, the scientific and technological development causes the epistemological notions to take on new determinations, demanding a restructuring and updating of the field of epistemology. From these assumptions, the present "Compendium" was projected as a basic reference book with entries arranged in alphabetical order on the most relevant theories, currents and concepts. But also as a work, without doubt, plural, capable of serving as a basis for the organization and development of epistemology in our cultural and academic context.