This study investigated older adults' peer teaching experiences at a Lifelong Learning Institute through interviews with eight teachers and observations of their classes. Thematic analysis revealed themes of peer-to-peer teaching, volunteer teaching, and explorative teaching. Discussion of the themes examines the meaning of older adults' peer teaching and finds that older adults consider their teaching a form of humanistic interaction and are motivated by a "busy ethic" as a social norm for retirement life. In addition, peer teaching is important for older adults as an experience of learning and discovery.