With the growth of online environments like MySpace, Second Life, World of Warcraft, Flickr, YouTube, Wikipedia, blogs, online support groups, and open source development communities, the web is no longer just about information. It is filled with social networks, multi-player games, and member-contributed content. This course, jointly taught by a computer scientist and a behavioral scientist, will examine how the social web operates, teach students how to build online communities, and help them understand the social impact of spending at least part of their lives online. We will examine what works and what fails to work in these online environments, and will use tools like Ruby on Rails and Drupal to build them. This class is open to advanced undergraduates and graduate students with either technical or non-technical backgrounds. Course work will include lectures and class discussion, homework, class presentations, and a group project.