This paper explores research and literature related to professional learning communities (PLCs) and describes their attributes and structures, the impact of different environments in which professional learning communities can be sustained, and the benefits for staff and students. There is consensus that PLCs can improve professional practice and efficacy as well as student learning and growth and that processes centered on teacher inquiry and decision making impact the effectiveness of PLCs. There are also increasing calls for structures and supports that facilitate the development of school cultures that encourage effective and sustainable PLCs. These supports are typically focused on the provision of time and flexible logistical structures within a school's organizational structures, the ability to form collaborative working relationships and the allocation of resources to develop leadership capacity and provide professional development support. Researchers agree that, within the context of a facilitative school culture, PLCs have the potential to significantly impact teacher practice, views of learning and student achievement. An extensive annotated bibliography provided. (Contains 7 tables and 119 endnotes.) [InPraxis Group Inc. developed this report for the School Improvement Branch, Basic Learning, Alberta Education.].