Principia Ethica is reprinted here with the previously unpublished Preface Moore wrote for a planned, but never completed, second edition. The volume also includes two important pieces from Moore's later ethical writing, 'Free will' and 'The conception of intrinsic value', and a new introduction by Thomas Baldwin.

First published in 1903, G. E. Moore's Principia Ethica is recognized as the definitive starting point for twentieth-century ethical theory.