Teacher leadership can be an important intervention for improving classroom instruction across K-12 public schools. Many researchers, policy-makers, and educators are calling for more teacher leadership. Yet, enhancing the impact of teacher leadership, in part, depends on a clearer understanding of the teacher leadership process. The ways in which teachers go about influencing the conditions within which they teach is a critical, yet understudied, part of that process. This dissertation examines teacher and faculty leadership activity, and relations among this activity with both school and classroom climate. This dissertation examined a statewide secondary data from a dataset with a unique set of variables that allowed for: (1) a descriptive examination of teacher and faculty leadership activity; (2) an investigation into sources of statistical variability across three conceptualizations of leadership activity; (3) the identification of teacher and faculty subpopulations; and (4) relationships between teacher and faculty leadership activity with both school and classroom climate. It used exploratory model building techniques including mixture modeling and logistic regression to make sense of multicollinear data in a clear and easily-accessible way with clear implications for research and practice. Foremost, results demonstrated that desirable school and classroom climates co-occur with schools' reliance on faculty leadership. That is, schools that relied more heavily on faculty for leadership were schools that also had better school and classroom climates. However, desirable climates co-occurred with only low-to-moderate levels of individual teacher leadership activity. Thus, the schools with the most desirable climates were those schools that heavily relied on their faculty for leadership but were filled with individual teachers engaging in only low-to-moderate amounts of leadership activity. Taken together, this dissertation demonstrated that teacher and faculty leadership can be an important intervention for improving the conditions within which they teach. It advanced the specification and operationalization of three key components of a teacher leadership process: teacher and faculty leadership, school climate and classroom climate. Each has implications for measurement, research, theory-building and practice. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]