This is the first collection of papers devoted to Ludwig Wittgenstein's cryptic but brilliant, On Certainty . This work, Wittgenstein's last, extends the thinking of his earlier, better known writings, and in so doing, makes the most important contribution to epistemology since Kant's Critique of Pure Reason - a claim the essays in this volume help to demonstrate. The essays have been grouped under four headings, reflecting current approaches to the work: the Framework, Transcendental, Epistemic, and Therapeutic readings.