G.E. Moore's Principia Ethica is a landmark publication in twentieth-century moral philosophy. Through focusing on the origin and evolution of his main doctrines, this guidebook makes it clear that Moore was an innovator whose provocative take on traditional philosophical problems ignited heated debates among philosophers. Principia Ethica is an important text for those attempting to understand and engage with some major philosophical debates in ethics today. The Routledge Guidebook to Moore's Principia Ethica provides a comprehensive introduction to this historic text, examining key Moorean themes including: ethical non-naturalism the naturalistic fallacy the Open Question Argument moral ontology and epistemology ideal utilitarianism vindictive punishment and organicity moral intuition for epistemic justification in ethics theory of value Ideal for anyone wanting to understand and gain perspective on Moore's seminal work, the book is essential reading for students of moral philosophy, metaethics, normative ethics, philosophical analysis, and related fields.