Wikis have recently been adopted to support a variety of collaborative activities within libraries. This article and its companion wiki, LibraryWikis (http://librarywikis.pbwiki.com/), seek to document the phenomenon of wikis in libraries. This subject is considered within the framework of computer-supported cooperative work (CSCW). The author identified thirty-three library wikis and developed a classification schema with four categories: (1) collaboration among libraries (45.7 percent); (2) collaboration among library staff (31.4 percent); (3) collaboration among library staff and patrons (14.3 percent); and (4) collaboration among patrons (8.6 percent). Examples of library wikis are presented within the article, as is a discussion for why wikis are primarily utilized within categories I and II and not within categories III and IV. It is clear that wikis have great utility within libraries, and the author urges further application of wikis in libraries.