This publication documents the role of social networking sites in all types of libraries such as school, college, university, public, special, and community libraries in the New Millennium covering the period 2000-2011. Each analysed entry highlights the usefulness of the article. Highlighted aspects of social networks include teens and young adults, privacy and trust, behavioural and social sciences, health sciences, and the role of Congress. This handy reference work and the literature it covers would enable libraries and decision makers to decide on how libraries can adapt social networks and for what ends, how much time and effort one should invest in these platforms, and how to monitor their success. Title, author, and subject indexes are an added pathway to the users of this book.