Web 2.0 technologies have introduced increasingly participatory practices to creating content, and museums are becoming interested in the potentials of 'Museum 2.0' for reaching and engaging with new audiences. As technological advances are opening up the ways in which museums share information about the objects in their collections, the means by which museums create, handle, process, and transmit knowledge has become more transparent. For this to be done effectively, however, some underlying contradictions must be resolved between museum practices, which privilege the account of the 'expert', and distributed social technology practices, whose strengths lie in allowing for many, sometimes contradictory, perspectives. This paper presents a theoretical position and framework for the adaptation of Web 2.0 technologies within the traditional work of the museum, in ways that support the generation and representation of knowledge in, by, and for diverse communities. We then expand on this theoretical perspective by discussing several case studies of exploratory work in this area, and close the paper by presenting a few tactical, bottom-up initiatives that museums and distributed communities can take to facilitate the diffusion of this new conceptual framework. Though the subject of this paper is on-line museums, the issues are relevant to all on-line collections, in particular portals, Online Public Access Catalogs (OPAC), and content management systems.