This study examined the strength and the direction of the relationship between principals' leadership behaviors and the development of professional learning communities, specifically teacher study groups. In effect, I sought to uncover principal leadership behaviors that positively affect the development of professional learning communities (PLC) in schools that received a Montclair State University Teacher Study Group Grant. Two surveys were distributed to teachers in participating schools and the completed surveys were analyzed through the use of descriptive statistics, correlation matrices, and multiple and simple regression models. The results from the study revealed that overall there is a strong relationship between principals' leadership practices and the development of professional learning communities. Additionally, the results from this study suggest that the combination of all the leadership practices measured by the Leadership Practices Inventory can help predict the development of professional learning communities. The results from this study will inform school principals of the leadership practices associated with successful professional learning communities, specifically teacher study groups. Further, the results from this study can be used to help guide professional development programs for educational leaders relative to the specific leadership practices that may help support a collaborative culture of professional learning communities in schools. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]