Among the early neo-classical economists, Francis Edgeworth is known as one of the most brilliant. Philip Mirowski now shows that Edgeworth is also one of the most misunderstood. Revealing for the first time some of Edgeworth's rarest writings, articles on psychic research and physics, and unpublished correspondence with noted intellectuals, Mirowski uses these texts to explain why Edgeworth abandoned the formalism for which he is remembered and never applied his newly forged statistical tools to neo-classical price theory. Emphasizing his latter turn toward probability theory, the selection of Edgeworth's papers broaden the interpretation of the relationship of the neo-classical program to physics, biometrics, physiological psychology, and other relevant sciences at the turn of the century. Mirowski has created an intellectual biography of this key figure that is unprecedented in scope.