Most current theories about collective cognitive activities in limited groups apply to structurally closed co-operative situations Here we propose to work in the framework of intellectual transactions and communities of action theory with a view to describing and designing CSCW systems which can be used in more structurally open situations. First we compare this approach with other theories of collective cognition (such as those focusing on situated cognition and communities of practice, distributed cognition and coordination mechanisms). We then present the core concepts involved in defining communities of action, the duality of goals and forms of knowledge and the operational, strategic, integrative and relational categories of collective activity on which the OSIR model is based. We conclude by presenting as an example the application of the model to a research project designed to assist the setting up of a health network.