The importance of close relationships for happiness has long been recognized. This long-held interest has produced an increase in relevant empirical work investigating the links between relationships and personal well-being in the last three decades. Recent attempts at integrating this vast body of literature suggest that responsiveness—i.e., the belief that close relationship partners understand, validate, and care for us—is a core process linking close relationships to health and happiness. In the present chapter, we review the links between responsiveness and happiness, with an emphasis on studies of marital and long-term romantic relationships. The available evidence indicates that partner responsiveness improves happiness in both negative contexts (by preserving happiness in the face of stress and adversity) and positive contexts (by augmenting and prolonging happiness induced by pleasant events and supporting the pursuit of personally meaningful goals and self-actualization). We believe that future work should build on this literature by investigating intergenerational effects of partner responsiveness on offspring happiness, comparing the roles of different social network members in happiness, examining how cultural grounding of relationships modulate the responsiveness-happiness link, and identifying the different components of responsiveness critical for happiness across cultures and developmental stages.