Basic research suggests that authenticity is a potential important antecedent of responsible organizational behavior and occupational health. However, ambiguities concerning the concept’s content and boundaries and measurement problems limit cumulative theory building and easy adaption in organizational research. We address these barriers by integrating existing conceptualizations into a two-dimensional model of authenticity comprising a self-directed and an expression-oriented dimension and developing and validating an instrument for organizational research. We furthermore use the newly developed scale to address two controversies in authenticity research: Order of causality between authenticity and well-being and health and self-other agreement on authenticity and its correlates. Results from multiple samples provide evidence for content, discriminant, and criterion validity, as well as internal and temporal consistency of the integrated short scale. Self-reports and others’ ratings support both dimensions’ relevance for work-related variables and revealed insights into how others estimate authenticity. Longitudinal data provided evidence for antecedents and consequences and uncovered differences in the malleability of the dimensions.