Positive affect, an index of psychological well-being, is a known predictor of functionality and health in later life. Measures typically studied include joy, happiness, and subjective well-being, but less often interest--a positive emotion with functional properties that differ from joy or happiness. Following differential emotions theory, the present study measured trait joy and interest in a population-based sample of 1,118 adults aged 65-86 years. As predicted, trait joy was associated with greater religious participation, while trait interest was associated with greater education. Joy was associated with lower morbidity and stress while interest was not. Interest was, in fact, associated with greater stress. Both emotions were positively associated with social support. We use the pattern of predictors to develop a functionalist conceptualization of these two emotions in later life, concluding that it is worthwhile to treat interest and joy as partially-independent positive affects contributing differentially to human emotionality and later life adaptation.