Background: Immersive virtual worlds are one of a range of different platforms that can be grouped under the concept of mediated environments, i.e. environments that create a metaphorical space in which participants can position themselves and be embodied. Synthesising the literatures concerning the various mediated environment technologies provides an opportunity for research regarding these various technologies to inform each other. Purpose: The variety of concepts and terms within the various literatures reviewed are used inconsistently. Various typologies are used, and these may overlap in part and yet contain elements others are missing. The purpose of this paper is to outline a conceptual framework that aims to bring these various typologies together into one overall reference model. This reference model is intended to support other researchers in the field by reifying the field of mediated environments, forming an agenda for negotiation, but also a basic introduction to the various aspects of mediated environments. Sources of evidence: The conceptual framework is primarily based on Activity Theory, with the various categories further subdivided through reference to the wider literature concerning immersive virtual worlds, webconferencing, multi-user dungeons (MUDs) and other text-based communication platforms. In addition to the categories included in Activity Theory, two key elements that typify mediated environments are their provision of a situated experience for the participant and an opportunity for the participants to create and perform an identity. These are not specifically addressed by Activity Theory, but are within the Communities of Practice model. The conceptual framework presented here merges these two models. Conclusions: The conceptual framework provides a useful basis for systematically reviewing the various aspects of mediated environments, and for further debate and development. (Contains 6 figures.)