In this holistic, descriptive, single-case study, the interactions of secondary literacy teachers who participated in the weekly #2ndaryELA Twitter chat were examined to explore the nature of online, self-selected, voluntary professional learning. Archived tweets from 17 chats occurring from July through November 2016, Twitter profile information, questionnaire responses, and semi-structured interviews with four participants were collected and analyzed. Wenger's (1998) social learning theory served as the theoretical framework, and the four main constructs--meaning, practice, identity, and community--were used as a lens through which the community interactions were viewed and interpreted. Four broad themes emerged from the data: Sharing, Connecting, Socializing, and Exploring. Participants shared ideas and resources most often. They made connections by interacting with and following others, and they socialized by sharing feelings and identifying with each other, which created a positive social climate. Participants explored new ideas through public reflection and negotiation of meaning very little. Findings revealed that the nature of learning in this environment is personalized and supportive, but there were obstacles to learning, such as the voluntary nature of participation and low levels of perceived efficacy. The Twitter chat structure was found to limit participants' depth of learning. A modified model of social learning theory is offered for use in voluntary, structured environments similar to Twitter chat communities. [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.]