This mixed-methods study explores how K-12 teachers use Twitter. An online survey was disseminated via Twitter to gauge their usage of, access to, and perceptions of Twitter. The results indicated that teachers highly value Twitter as a means of self-directed professional development. Respondents who reported using Twitter multiple times a day were more likely to use it for professional purposes than personal ones. Chief among the reported perceived benefits were professional development and meaningful relationships that teachers formed with other teachers who use Twitter. Implications for practice, including the ability for teachers to seek professional development for their specific needs, are discussed.