Library 2.0 (L2) is a transformation in the way library services are delivered to library users. It provides new tools to make the library space (both virtual and physical) more interactive, collaborative and driven by community needs. It encourages collaborative two-way social interactions between library staff and library customers. L2 requires user participation and feedback in the development and maintenence of library services.
The phrase was coined by Michael Casey in his blog, LibraryCrunch, in 2005, although the concepts that collectively make up "Library 2.0" existed well before then. The term was a spinoff of "Web 2.0" which had been coined by O'Reilly Media.