Web 2.0 technologies provide school administrators the opportunity to offer teachers meaningful professional development. The purpose of the qualitative case study was to investigate ways in which U.S. K-12 public school teachers who participated in weekly Twitter Edchat discussions perceived the use of a social network site for professional development. The research design was a qualitative embedded case study that included 17 U.S. K-12 public school teachers who participated in at least two weekly Twitter discussions over 3 consecutive months. Study participants' work experience ranged from 1-36 years. Data collection included a review of the literature, pilot study, semi-structured interviews, and participants' archived online posts. Regardless of teachers' feelings toward their workplace, participants believed participation promoted sense of belonging and positive attitudes toward teaching. Study findings included teachers' perceptions of the technical benefits and drawbacks related to using a social network site for professional development. Findings for this study included the digital habitat for teacher professional development and social network sites model, a guide for educational leaders in understanding how and why a social network site may support teacher professional development. [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.]