In times of exponential change, high quality, cost-effective teacher professional development is an urgent need that personal learning networks (PLNs) promise to address. The purpose of the qualitative case study was to (a) explore, understand, and describe how PreK-12 educators, who are members of The Educator's PLN and Classroom 2.0 communities, used their PLNs for professional development; and (b) describe what components of a PLN the educators viewed as critical to their success and, ultimately, to student success. An embedded multiple two-case case study research design was used to achieve the purpose, including 10 PreK-12 educators who were active and engaged users of PLNs drawn from two different PLN sites. Data collection included a quantitative survey, semi-structured interviews, think-aloud exercises, and documentary data. Revealed in the findings was that participants used a variety of digital tools to create personalized learning environments within which they were able to forge meaningful connections with large networks of others as they gathered and shared resources, engaged in discussion, collaborated, applied new learning, gave and received support, and advanced their careers. Participants in the study perceived institutional support as a critical factor involved in their successful use of a PLN for professional development purposes. In the absence of such support, highly motivated and digitally literate educators were still able to take advantage of PLNs to transform their teaching, suggesting that for educational leaders to leverage the potential of PLNs for teacher professional development and enhanced student learning, they must actively promote and support their use. [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.]