For many years, those who work in the mentoring field have wondered how they can extend the impact of their programs beyond the benefits experienced by young people they serve. There has been an increasing desire within our field to harness the power of mentoring to enable the youth served in a program to not just grow individually, but to collaborate and partner with one another, their mentors, and program staff, to use their talents and voices to influence wider positive changes in their communities. This resource highlights one potential path to this extended impact of mentoring programs: youth participatory action research (YPAR). "YPAR is uniquely suited as an approach to implement within mentoring contexts and offers a wide array of benefits like": (1) Promoting positive change within youth programs and communities; (2) Building youth skills and guiding what mentors and youth do together; (3) Positively impacting youth and adult participants (e.g. enhancing trust-building in mentoring relationships, supporting youth's interest in issues that are important to them); and (4) Supporting evaluation of the mentoring program itself. In the guidebook, readers can discover more about the background and benefits of YPAR, information on the process and guidance for using the approach, planning worksheets for adults in mentoring programs to get started, and more! [The Starbucks Foundation provided support for this guidebook.]