In this study, we examined the characteristics of adolescents’ deep interests or ‘‘sparks,’’ the role of relationships in supporting the development of sparks, and whether having a spark was associated with positive developmental outcomes. Participants included 1,860 15 years olds from across the United States who participated in the national Teen Voice survey (56% European American, N1⁄41,860). Profile-centered analyses suggested that sparks are characterized by the intensity of positive feelings, immersion, and utility. The strongest sparks were associated with pursuits requiring more interpersonal engage- ment, such as sports, drama and dance, participating in politics, and serving others. Spark intensity was related to better social, academic, and affective outcomes. Addition- ally, youth with stronger sparks reported more encouragement, financial support, and transportation to spark activities from parents, mentors, extended-family, neighbors, school-based adults, and peers. Benefits of adolescents’ engagement in interest-driven activities and the role of caring relationships in supporting such interests are highlighted.