This review surveys and synthesizes the findings of 87 focal pieces, published primarily since 2009 and mid 2018, on the formal and informal use of social media--blogs, wikis, and social networking--for second and foreign language teaching and learning (L2TL), including studies on the use of educational sites like Livemocha and Busuu and vernacular sites like Facebook and Twitter. The article frames the review in the development of social media and the history of social computer-assisted language learning (CALL) research. Synthesis identifies common findings, including that social media can afford the development of intercultural, sociopragmatic, and audience awareness, language learner and user identities, and particular literacies. Presentation of the focal pieces and common findings is intertwined with discussion of problematic issues, and each section concludes with a summary and implications for future research and practice.