This article discusses L. W. Sumner's theory of well-being as authentic happiness. I distinguish between extreme and moderate versions of subjectivism and argue that Sumner's characterization of the conditions of authenticity leads him to an extreme subjective theory. More generally, I also criticize Sumner's argument for the subjectivity of welfare. I conclude by addressing some of the implications of my arguments for theories of well-being in philosophy and welfare measurement in the social sciences.