Having a noble purpose in life is an important component of positive youth development; however, little is known about how noble purposes develop over time. Therefore, using three waves of interviews over a 5-year period with 9 adolescents (N = 9) who demonstrated intense commitments to various noble purposes, the present study developed a grounded theory of the development of noble purpose, including a focus on how commitment was initiated, sustained, increased, and changed over time. Results revealed the exemplars made commitments early in life. With the exception of triggering experiences, which immediately intensified their level of commitment, commitment generally grew slowly but steadily in response to positive feedback. Mentors and like-minded peers played an important role in supporting noble purposes over time, and access to new resources led exemplars to expand their focus. Implications for supporting the development of noble purposes are addressed. (Contains 2 tables.)