It is well established and understood that teacher professional development (PD) is necessary for the advancement of education. This professional training can lead to improved teacher self-efficacy and higher student achievement. Despite recent initiatives to advance teacher PD to address changes in standards-based teaching and learning, national reports have shown that many states fail to offer adequate PD to their teachers. Online informal professional development may allow some teachers to supplement meager formal PD offerings. This project demonstrated the possibilities of using one social networking site (SNS), Twitter, for informal PD. The purpose of this action research was to understand the experiences of teachers who used Twitter for informal PD. Three PD sessions on educational uses of Twitter were planned and presented to thirty elementary school teachers to illustrate how to navigate Twitter's interface along with ideas for building a professional network through the application. Seven teachers who took part in the PD sessions participated in two semi-structured interviews, which provided information about how they used Twitter and how they perceived this SNS for professional learning purposes. This data was open coded and analyzed through a systematic, multi-step process. Data revealed common actions of novice Twitter users as they built their networks, but also perceived benefits and challenges of using Twitter for professional learning. Participants had an overall positive perception of Twitter as a PD tool, but many found limitations with Twitter's interface and with their own personal barriers to engaging with others through the application. From this data, considerations for future PD devoted to Twitter are discussed along with several recommendations for alleviating the first- and second-order barriers to teachers using Twitter for PD. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]