Keith Lehrer introduces students to the main classical and modern accounts of knowing in this outstanding second edition of Theory of Knowledge. Lehrer starts with the conventional definition of knowledge as justified true belief and then explores the truth, belief, and justification conditions before thoroughly examining foundation theories of knowledge, Platinga's work, externalism and naturalised epistemologies, internalism and contemporary coherence theories, contextualism, and contemporary reliabilist and causal theories. Lehrer carefully considers all points of view and comes to the conclusion that in order to produce knowledge, adequate internal and external components must be matched.