Positivity resonance refers to moments of interpersonal connection characterized by (1) shared positive affect, (2) behavioral and biological synchrony, and (3) mutual care. We measured positivity resonance as a latent construct indicated by new measures of its defining features to predict concurrent and future relationship satisfaction. Long-term married couples (N=156) engaged in a 15-minute conflict conversation. Couples were videotaped for subsequent behavioral coding; their peripheral physiology was recorded second-by second; and they later provided continuous ratings of their own affect during the conversation. Behavioral, physiological, and subjective measures of the defining features were developed, demonstrated as reliable, and included in a measurement model of positivity resonance. Confirmatory factor analysis indicated that this model had excellent fit. Next, we tested the association between the latent construct of positivity resonance and marital satisfaction (measured via standard self-report inventories). As hypothesized, positivity resonance was significantly associated with both husbands’ (.21 < all βs < .28; all ps < .019) and wives’ (.23 < all βs < .32; all ps < .013) concurrent and future marital satisfaction (assessed 5 and 10 years after the initial conversation). Results offer insight into the behavioral and biological pathways through which strong relationships are built and maintained.