The authors propose the Model of Self-Determined Sexual Motivation to examine sexual motivation in dating relationships using a Self-Determination Theory (SDT) framework. This model predicted that sexual need satisfaction would mediate the association between self-determined sexual motives and the outcome variables of psychological well-being and relational quality. Three studies tested this model. Study 1 was a cross-sectional study that investigated sexual motivation in dating relationships. Study 2 was an event-contingent interaction record study that investigated specific sexual interactions over 2 weeks. Study 3 combined event- and interval-contingent methods using a daily diary to examine the model for both partners to enable examination of actor and partner effects. Discussion section focuses on the power of examining SDT in the sexual domain.