This book is the first comprehensive treatment of Quine's brief yet memorable foray into ethics. It defends Quine against his most formidable critics, corrects misconceptions in the reception of his outlook on ethics as a philosophical enterprise and morality as a social institution, and restores emphasis on observationality as the impetus behind his momentous intervention in metaethics. The central focus is on Quine's infamous challenge to ethical theory: his thesis of the methodological infirmity of ethics as compared with science. The book ultimately demonstrates that the challenge is not only valid but also valuable in its identification of opportunities for reformation in ethical reasoning and moral justification.