Implementation of Professional Learning Communities (PLC), as described by DuFour (2006), has depended upon a balance between teacher buy-in and administrative fiat. The tension between the "bottom-up" character of the former and the "top-down" character of the latter presents a leadership challenge: meeting students' learning needs requires decentralized, shared decision-making on the part of the teachers who work directly with individual students, while those same teachers are subordinates in a hierarchy that centralizes authority at the top of the organization chart. PLC literature lacked a theoretical model that reconciled these seemingly disparate roles. The Literature Review introduced Complex Adaptive Systems (CAS) modeling, and noted some "prima facie" similarities between Professional Learning Communities and Complex Adaptive Systems. The study's central purpose was to explore whether those similarities, those links, were strong enough to conclude that Professional Learning Communities are a form of Complex Adaptive Systems. The study systematically analyzed the terms and concepts used to introduce DuFour's PLC model, and the terms and concepts used to explain Complex Adaptive Systems by Holland (1992), Gell-Mann (1994) and others. The terms from both domains were then systematically compared. The study concluded that Professional Learning Communities are indeed a form of Complex Adaptive Systems, though with a caveat: they are a form of Complex Adaptive Systems when they function as Complex Adaptive Systems. This is to say that a Professional Learning Community, as described by DuFour, is optimally implemented and functioning when it is behaving as a Complex Adaptive System, focusing on simple "rules" (i.e., PLC Essential Questions) on the local level that yield unified behavior on the global level. The leadership implications of these findings indicated that a focus on the Essential Questions, and not "PLC formation," would be the most effective practice for PLC leadership, and that teacher buy-in could be enhanced if Professional Learning Communities are viewed as belonging to a larger class of activities that are observed in other fields, some of which are described in the study. Implications for further study include using CAS modeling as a means of determining the degree to which Professional Learning Communities are being implemented, and having CAS modeling serve as the basis for a conceptual framework for PLC implementation. [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.]