This book maps the terrain of the part of ethics that reflects on the nature of ethics itself, a field known as metaethics. It helps upper-level undergraduates and other interested readers understand the main theoretical innovations as reactions to puzzles about moral disagreement, reference, moral epistemology, metaphysics, and moral psychology. The book provides the necessary background to grasp the puzzles and to understand the solutions offered. More complex positions are displayed as developments of simpler ideas and theories. Positions covered include error theory, subjectivism, relativism, noncognitivism, fictionalism, supernaturalism, nonnaturalism, and naturalism. Several charts map the relations between the positions. Key Updates to the Second Edition:A text that is easier to follow throughout, now with regular references to the main explanatory chart in the IntroductionAn expanded and more self-contained discussion of supernaturalism, which now can be better used as its own module or omitted completely from a class syllabusAdditional understanding and/or extension-oriented questions at the end of almost every chapterUpdates to citations and Suggested ReadingsReassurances to the student reader that uncertainty about certain difficult topics is both natural and expected