This study developed identification measures between U.S. Service Academy cadet squad members and squad leaders in peer-mentoring relationships, highlighting identification as an important antecedent to mentoring. However, research has failed to show evidence of this relationship, largely because researchers have failed to measure identification, psychometrically test their measures, or differentiate identification from related constructs. Addressing this gap, we use theories of the self and interviews of cadets and faculty members to develop measures of both mentee and mentor identification. We include these measures, along with measures of empathy and similarity, in a longitudinal study of mentoring between cadet squad leaders (n = 96) and squad members (n = 968). Factor analyses revealed a three-factor solution of mentee identification with the mentor, measuring identification, empathy, and similarity. The analyses yielded a four-factor solution of mentor identification with the mentee, measuring two forms of identification, self-image, and empathy. The findings encourage future research to employ these measures for exploring identification's role in mentoring relationships.