Youth mentoring is an individualized and versatile intervention that can respond to the needs and circumstances of each mentee. Given the flexibility of this relationship-based approach, formal programs have designed and implemented various modes and models of mentoring. Consequently, the field of youth mentoring is broad and diverse with unclear boundaries regarding what constitutes “mentoring.” In this chapter, we attempt to define the fundamental nature of mentoring. We then review multiple frameworks that have been proposed to characterize important dimensions that distinguish different types of mentoring relationships and different types of mentoring programs. Next, we offer an integrative typology to conceptually organize formal youth mentoring programs by their salient features. Finally, we apply this typology to situate the Friends of the Children program within the field of youth mentoring and to highlight the distinctive nature of its long-term professional mentoring model.