This qualitative multiple case study examines how principals contribute to the success of exemplar elementary PBIS schools in North Carolina and how their thoughts about PBIS informed their actions. Guided by the literature on principals and change efforts and sensemaking, this study used individual interviews, focus group interviews, field notes, questionnaires, and physical artifacts to understand how and why principals facilitate the successful implementation of a PBIS program in their respective schools. Data analysis included within-case analysis and cross-case analysis to identify and juxtapose emergent themes. The findings revealed that principals contribute to the success of their schools by making PBIS a priority, reinforcing expectations, analyzing data, attending meetings, supporting the staff, effectively communicating and collaborating with stakeholders, and gaining stakeholder buy-in. Principals also spent time advocating for the program, monitoring implementation, supporting staff, showcasing and celebrating milestones and creating strong committees. This study also provided explicit examples of how principals go about implementing the PBIS program in areas identified by the SET and demonstrate how schools maintain momentum in sustaining PBIS when there is principal turnover. The attributes of sensemaking most prominent were social, plausibility rather than accuracy, focused on and by cues, identity construction, and enactive of sensible environments. The results suggest that enhanced training programs for principals, details about successful practices, and support for district initiatives facilitate the success of the PBIS. [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.]