This study encompasses research on the role of mentoring in the experiences of instructional supervisors in K-12 school districts and how mentoring contributed to their professional development. The method used for this research included a questionnaire, one-to-one interviews, and a panel discussion to capture the essence of the work of the instructional supervisor. The nine instructional supervisors involved in this research study demonstrated the importance of relationships and informal mentoring, and discussing this as a group contributed to the validity of the findings in the one-to-one interviews. Elizabeth McKinsey’s three-phase mentoring framework was applied to this research study. The eight themes that emerged in this study, just within the scope of professional development and the role of mentoring, produced a tremendous body of qualitative research. This research study produced five strong implications for practice regarding the role of mentoring experiences for instructional supervisors. The implications for practice include the value of relationships in mentoring, the proximity of instructional supervisors who fostered informal mentoring, the importance of the knowledge that the mentor has when working with a mentee, the role of agency or control of choice for the mentee, and finally emphasizing preservice work for prospective instructional supervisors. Each of these implications for practice is well-supported by the current literature and the research that this study contributes to the field.