--- - |2 Abstract This research provides the first empirical investigation of how approach and avoidance motives for engaging in sex in intimate relationships are associated with personal well‐being and relationship quality. A 2‐week daily experience study of college student dating couples tested specific predictions from the theoretical model and included both longitudinal and dyadic components. Whereas approach sex motives were positively associated with personal and interpersonal well‐being, avoidance sex motives were negatively associated with well‐being. Engaging in sex for avoidance motives was particularly detrimental to the maintenance of relationships over time. Perceptions of a partner's motives for sex were also associated with well‐being. Implications for the conceptualization of sexuality in relationships along these two dimensions are discussed. - Personal Relationships, Page 465-482, October 2018.