The purpose of our study was to examine mentors' conceptualizations of mentoring residents (preservice teachers) in a teacher residency program. Understanding the nuances of mentoring in a year-long placement in a mentor's classroom may further illuminate mentoring in this context. In this qualitative, longitudinal study, we used constant comparative analysis to allow the data to drive recurring patterns and ideas linked to real-life situations and values coding to examine mentors' conceptualizations of mentoring in a residency program. Residents enrolled in the federally-funded Teaching Residency Program for Critical Shortage Areas program were placed in a high-need urban secondary school for a year-long clinical experience to work alongside mentors, who had a non-evaluative role. By examining mentors' conceptualizations of mentoring in this particular context, our data reveal aspects of their agency that reflected three main themes: (a) professional altruism, (b) extant knowledge, and (c) resident as stimulus. Our findings add to the research on mentoring by illuminating the voices of mentors to describe how they conceptualized mentoring and to further examine their motivations for mentoring, contributions to the mentee, and professional gains.