The Social Media Reader is now available as a Creative Commons licensed PDF on Archive.org. The book is CC BY-SA-NC licensed; all but one of the chapters are CC BY-SA or CC BY. Archive.org also hosts an EPUB and Kindle version as well.
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The Social Media Reader (ed. Michael Mandiberg) is a collection of essays exploring the rise of participatory culture, and the ensuing blurring of the boundaries between creators and audiences. The book features key essays from the major authors in the field, including Chris Anderson, Yochai Benkler, danah boyd, Henry Jenkins, Lawrence Lessig, Tim O'Reilly, Jay Rosen, Clay Shirky, and Siva Vaidhyanathan.