Web 2.0 and social media applications such as blogs, wikis and social networking sites offer the promise of a more vibrant, social and participatory Internet. There is a growing interest within the library community in debating the potential impact that such services might have within libraries and such debates have gathered around the moniker of `Library 2.0'. To date, however, there has been little theoretical work and there is a need to develop more formal definitions and frameworks. This editorial discusses the origins of the term Web 2.0, provides a structured framework for rationalizing the implications of Web 2.0 services and outlines some of the areas in which librarians are positioned to provide a unique contribution to the further development of such services.