This article provides a critical analysis of the teacher leadership literature. It considers teacher leadership within the context of contemporary leadership theory, focusing particularly upon distributed leadership. The article explores different interpretations and definitions of the term "teacher leadership" and considers the implications for professional practice. Drawing upon recent reviews of the literature, it focuses upon the impact and effects of teacher leadership at three levels: the school, teacher, and student. It highlights some of the barriers to teacher as leaders and some of the ways in which teacher leadership can be developed and supported. The article concludes by outlining future directions and challenges for research in this field.