This qualitative case study examines the relationship of teachers who mentor other teachers. We studied 125 autobiographical portfolios submitted by elementary and secondary teachers who had won awards as outstanding educators from their campuses and were competing at the district level. The research site was a midsize city (population 95,000) in southwest Texas. Findings support the view that effective mentoring is a continuing collaboration leading to lifelong learning and professional interdependence. The findings suggest that retention of teachers requires active involvement, whether formal or informal, and that teachers who mentor have a strong sense of responsibility toward preservice teachers, their peers, and the future of education. Via a grounded theory methodology, categories emerged leading to the development of a theoretical framework. This framework describes the effects of mentor relationships occurring throughout the teachers' lifetimes--that is, what is defined as transgenerational mentoring.