The role middle school building leadership teams have in professional development (PD), through a distributed leadership model, was explored in this multiple-case study. There is minimal research regarding the impact of middle school building leadership teams (BLTs) related to their responsibilities of professional development. The intent of this study was to add to the body of research regarding the role that middle school BLTs, beyond the principal alone, have on designing and delivering professional development. Through a qualitative research design, data were collected through one-on-one interviews, focus group interviews, observations, and document collection. The findings illuminated four major themes of BLT work in professional development: designing and delivering professional development, building capacity, mentoring new teachers, and the lack of time to accomplish goals. The significance of the research highlights the importance of a distributed leadership model in BLT activities with a focus on professional development. Additionally, the middle school BLT structure could take the responsibility of sole instructional leader off of the principal and distribute the responsibility among administrators and teacher-leaders. The findings provide principals valuable insight regarding the collective influence of a BLT related to professional development. The structure of the BLTs in this study could be replicated by other middle schools to enhance their professional development programs. [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.]