Cooperation Metaphors are sets of rules to support interaction and collaboration between users who want to explore complex content and information together. The rules determine how the collaborative community can be created and managed, how members of the community can operate on their own or can cooperate with other members. Different types of situations, tasks and user roles determine different behaviours and therefore need different metaphors. The paper will present the general issue, describing in general what cooperation metaphors are and how they can be defined. A number of examples, related to typical activities for virtual museums (i.e. museums on the Web) will be used in order to give a practical understanding of what cooperation is, or can be. The paper will also argue that virtual metaphors lack some of the features of real-life cooperation, but, on the other hand, can also offer unexpected, powerful and effective possibilities not available in (traditional) real-life. Finally, the paper will describe how collaborative activities for virtual museums can be implemented using today's tools and applications for collaboration on the Web; such as Net2gether, Microsoft Research's Virtual Worlds, and the WebTalk series.