This qualitative multiple case study sought to understand staff members' perceptions of the components of an effective and sustainable professional learning community. The Professional Learning Community Assessment questionnaire and interviews were the instruments utilized to attain data. The study's results allowed the researcher to identify areas of strength and areas of weakness that were integral aspects of each learning community's operation. Specifically, the study included 22 participants across three middle school study sites. There were 12 key findings that emerged from the data across the three study locations. The findings revealed the need for regular collaboration, supportive leadership practices, a clear vision and a distinct set of values to guide learning community members. Additionally, the findings highlighted the beneficial aspects of professional learning communities but revealed the need for refinement related to adequate meeting time, supportive structures, and planning. Future research should be conducted across a longer time period with a larger sample size to ascertain if the findings are similar to those that arose from this research. Finally, a recommendation of adding an evaluative component to the learning community was made. This will enable school administrators to regularly monitor the progress of the PLC. This study will support positive change and will provide valuable data that can be utilized at each of the study sites to promote a school culture of collaboration, academic success, and collegiality. This research may potentially result in a more well-organized learning environment. The findings may serve as the impetus for sustained change and an atmosphere that influences teacher and student learning. [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.]