DescriptionOngoing interest in teachers as a source of leadership has led scholars and practitioners to seek definitional clarity around the term “teacher leadership” and to better understand both the teacher leader and the work the teacher leader does. This qualitative study investigated the experiences of informal teacher leaders in an effort to contribute to the body of research concerned with how teacher leadership is enacted and cultivated. For this study, informal teacher leaders were defined as full-time classroom teachers who also take on leadership work without formal leadership titles to designate those roles. Research questions were as follows: 1) How do informal teacher leaders define and conceptualize teacher leadership? 2) Why do informal teacher leaders engage in leadership? 3) How do informal teacher leaders perceive the impact of their work? 4) What factors influence informal teacher leaders’ leadership work? Data collection consisted of semi-structured phone interviews with 10 participants who self-identified as teacher leaders. Findings from this study provide important insights into key components of informal teacher leadership. First, informal teacher leaders go above and beyond their job description to engage in professional learning, collaboration, and advocacy. These three dimensions combine to operationalize a definition of informal teacher leadership. Second, informal teacher leaders understand their work as being accessible to all and focused on collective capacity building. These beliefs stand in contrast to conceptualizations that focus primarily on the role and characteristics of an individual as a source of teacher leadership. Third, informal teacher leaders are motivated by their deep commitment to learning, community, and the profession, which compel them to action despite disincentives. Fourth, informal teacher leaders perceive their impact to be most clearly evidenced in the changed attitudes and behaviors of their colleagues. Fifth, informal teacher leaders report their work is most directly impacted by the following conditions: their status as classroom teachers, relationships with colleagues, principal or administrative influence, and time constraints