Platforms like Facebook, Wikipedia, YouTube, and Twitter have significantly changed the internet in recent years. They are considered social media because they have a major influence on how people present themselves and their interests online, how they maintain and form relationships, and how they inform themselves about relevant topics. At the same time, they raise a number of far-reaching questions: Does social media eliminate privacy? Does social media make everyone a journalist? Does social media provide knowledge for all? Are social media participatory, or do they monitor and control people? This volume addresses these questions from a communication sociology perspective, providing an overview of how social media is transforming our individual daily lives as well as our society. The second edition has been updated and expanded.