This research tested 6 models of the independent and interactive effects of stable personality traits on each partner's reports of relationship satisfaction and quality. Both members of 360 couples (N = 720) completed the Multidimensional Personality Questionnaire and were interviewed about their relationship. Findings show that a woman's relationship happiness is predicted by her partner's low Negative Emotionality, high Positive Emotionality, and high Constraint, whereas a man's relationship happiness is predicted only by his partner's low Negative Emotionality. Findings also show evidence of additive but not interactive effects: Each partner's personality contributed independently to relationship outcomes but not in a synergistic way. These results are discussed in relation to models that seek to integrate research on individual differences in personality traits with research on interpersonal processes in intimate relationships.