Teacher leadership has been recognized as a necessary ingredient to support educational reform efforts. Leaders provide the needed expertise to ensure reforms are successful in promoting student learning. The overarching goal of the "Leadership in Freshman Physics" program is to support a cadre of teachers-leaders who will become advocates for "Physics First" by developing their knowledge of physics content and research-based pedagogy. In order to support teachers in developing the knowledge, skills, and dispositions for effective leadership, it is important to first understand their initial views of teacher leadership and their prior leadership experiences. In this paper we present results from the initial phase of our multi-year research study in which we examine definitions of teacher leadership, teachers' past leadership experiences, and teachers' views of themselves as leaders. Participants include a cohort of 36 teachers participating in the program, each of whom has committed to teaching a year-long freshman physics course at his/her school. Our findings indicate teachers' definitions of leadership are relatively narrow, and often confined to formal leadership roles. Though teachers participate in numerous leadership activities, they don't explicitly consider these to be leadership. Implications for addressing teachers' conceptions through professional development are shared. (Contains 2 tables and 2 figures.)