Web 2.0 technologies empower individuals to contribute thoughts and ideas rather than passively survey online content and resources. Such participatory environments foster opportunities for community building and knowledge sharing, while encouraging the creation of artifacts beyond what any single person could accomplish alone. In this chapter, we investigate the emergence and growth of two of such environments: the highly popular Wikipedia site and its sister project, Wikibooks. Wikipedia has grown out of trends for free and open access to Web tools and resources. While Wikipedians edit, contribute, and monitor distinct pieces of information or pages of documents, Wikibookians must focus on larger chunks of knowledge, including book modules or chapters as well as entire books. Several key differences between these two types of wiki environments are explored. In addition, surveys and interviews, conducted with Wikibookians, shed light on their challenges, frustrations, and successes.