Wittgenstein’s last work, On Certainty, is widely regarded as his third masterpiece of philosophy and one of his most enigmatic writings. On Certainty explores the ways in which claims of indisputable knowledge are expressed, and how language forms the basis of such claims. On Certainty has largely been read as representing a break with Wittgenstein’s previous thinking, but this study places these ideas firmly in the development of his thought since the 1930s. Wittgenstein on Certainty and Doubt illuminates Wittgenstein’s examination of the logical features of epistemic terms-such as ‘know’, ‘believe’ and ‘doubt’-and his interrogation of the foundations of human knowledge, the extent to which our knowledge is immune from doubt, and the conflicts between different articulations of knowledge.