Vallerand et al. (2003) developed a dualistic model of passion, wherein two types of passion are proposed: harmonious (HP) and obsessive (OP) passion that predict adaptive and less adaptive interpersonal outcomes, respectively. In the present research, we were interested in understanding the role of passion in the quality of coach–athlete relationships. Results of Study 1, conducted with athletes (N = 157), revealed that HP positively predicts a high-quality coach–athlete relationship, whereas OP was largely unrelated to such relationships. Study 2 was conducted with coaches (N = 106) and showed that only HP positively predicted the quality of the coach–athlete relationship. Furthermore, these effects were fully mediated by positive emotions. Finally, the quality of the coach–athlete relationship positively predicted coaches’ subjective well-being. Future research directions are discussed in light of the dualistic model of passion.