Nostalgia, a sentimental longing for one’s past, predicts or augments psychological wellbeing (PWB). We hypothesized that it does so—at least in part—via authenticity, a sense of alignment with one’s true self. We obtained support for this hypothesis in four studies. Using a measurement-of-mediation design, across a Western (United States) and East-Asian (China) culture, we found that nostalgia is associated with both authenticity and PWB, and that the nostalgia-PWB link is mediated by authenticity (Study 1, N = 611). Using an experimental-causal-chain design, we showed that nostalgia increases authenticity across U.S. and Chinese samples (Study 2, N = 777). We then demonstrated that authenticity increases PWB on a domain-general measure (Study 3, N = 596, U.S. sample). Finally, we clarified that the benefits authenticity confers on PWB are domain general rather than domain specific (Study 4, N = 414, U.K. sample). This research represents the first attempt to address systematically the path from nostalgia to PWB via authenticity. We discuss implications for the broader literature.