This book provides recent scientific information on the philosophy of Ludwig Wittgenstein (1889-1951). It is a new contribution that will provide the reader with an introduction to the epistemological reflections present mainly in the writings published under the title On Certainty. The book's structure is as follows: the first chapter presents some structural aspects of On Certainty; the second chapter focuses on the interpretations of commentators Avrun Stroll, Rush Rhees and Danièle Moyal-Sharrock on the themes of foundationalism and scepticism; and the third chapter emphasises the question surrounding the so-called 'third Wittgenstein' and some of the many questions that arise from it.