This article describes the need for additional cross-cultural study of teacher leadership. A rationale for researching teacher leadership is presented based on the need to provide clarity to the definition of the concept and to understand better how to facilitate teacher leadership development. A primary research question is shared: “How is teacher leadership conceptualized and enacted and what are the implications for educational stakeholders?” A set of attributes and indicators of teacher leadership is provided based on a review of literature focusing on teacher leadership. Then four additional concepts related to teacher leadership are described—formal and informal influence, school culture, school improvement, and professional development—followed by a summary of cautionary considerations. Finally, a multi-stage research design is presented in support of the International Study of Teacher Leadership, a cross-cultural examination of teacher leadership.