This article describes the development of a measure of dispositional authenticity and tests whether authenticity is related to well-being, as predicted by several counseling psychology perspectives. Scales were designed to measure a tripartite conception of authenticity, comprising self-alienation, authentic living, and accepting external influence, which was supported with exploratory factor analysis. Multigroup confirmatory factor analysis showed that the factor loadings were invariant across sample, ethnicity, and gender. The scale showed substantial discriminant validity from the Big Five personality traits, nonsignificant correlations with social desirability, and 2- and 4-week test-retest correlations ranging from r = 0.78 to 0.91. Each subscale was strongly related to self-esteem and aspects of both subjective and psychological well-being. This article provides the first direct test of several theoretical models that view authenticity as integral to well-being. (Contains 2 figures and 8 tables.)