The current research reports a dyadic analysis of sexual satisfaction, relationship happiness, and correlates of these couple outcomes in a large multinational dataset consisting of 1,009 midlife heterosexual couples (2,018 individuals) recruited in Japan, Brazil, Germany, Spain, and the United States (Heiman et al., 2011). Actor-Partner Interdependence Models (Kenny, Kashy, & Cook, 2006) identified correlates of sexual satisfaction that included individuals' reports of good health; frequent kissing, cuddling, and caressing; frequent recent sexual activity; attaching importance to one's own and one's partner's orgasm; better sexual functioning; and greater relationship happiness. Even after controlling for individual-level effects, partners' reports of good health; frequent kissing, cuddling, and caressing; frequent recent sexual activity; attaching importance to one's own and one's partner's orgasm; better sexual functioning; and greater relationship happiness contributed significantly to predicting and understanding individuals' sexual satisfaction. Correlates of relationship happiness included individuals' reports of good health; frequent kissing, cuddling, and caressing; frequent recent sexual activity; attaching importance to one's own and one's partner's orgasm; better sexual functioning; and greater sexual satisfaction, and once again, even after controlling for individual-level effects, partners' reports of each of these correlates contributed significantly to predicting and understanding individuals' relationship happiness. Interactions of individual and partner effects with participant gender are also reported. Current results demonstrate empirically that the partner "matters" to an individual's sexual satisfaction and relationship happiness and indicate that a comprehensive understanding of factors contributing to these couple outcomes requires a couple-level research strategy. Partner effects, even when controlling for individual effects, were consistently observed, and explanation of sexual satisfaction and relationship happiness always depended on identifying and understanding mutual and concurrent individual and partner influences.