Having or developing a sense of purpose is an important component of positive adolescent development. However, there is limited empirical understanding of how youth purpose develops and what aspects of youth’s ecologies best support purpose development during adolescence. This chapter seeks to provide insight into how significant adults, both parents and non-parental adults, serve as ecological assets that may support purpose development for youth during adolescence. We begin by discussing how developmental and ecological theories can inform the broader literature on youth purpose. We then present findings from a study examining the development, characteristics, and influence of youth–adult relationships across multiple contexts and over key transition points across adolescence, focusing on the ways in which relationships with parents and other significant adults can play a key role in cultivating and nurturing purpose development during adolescence. We close by discussing implications for understanding effective ways of supporting purpose development during adolescence and the benefits of mixed methods research for those aims.