This edited collection explores the philosophy of Clarence Irving Lewis through two major concepts that are integral to his conceptual pragmatism: the a priori and the given. The relation between these two elements of knowledge form the core of Lewis’s masterpiece Mind and the World-Order. While Lewis’s conceptual pragmatism is directed against any conception of the a priori as constraining the mind and experience, it also emphasizes the inalterability and the unavoidability of the given that remains the same through any interpretation of it by the mind. The essays in this volume probe Lewis’s new account of the relation between the a priori and the given in dialogue with other notable figures in 20th-century philosophy, including Carnap, Friedman, Goodman, Putnam, Quine, Russell, Sellars, and Sheffer. C.I. Lewis represents a focused treatment of a long-neglected figure in 20th-century American philosophy.