The paper proposes a refinement of the concept of 'Common Information Spaces' (CIS), which has been proposed as a conceptual framework for the CWCW field in order to provide analyses of cooperative work. The refinement is developed through an introductory discussion of previous analyses of CIS and on the basis of a thorough description of the CIS of a hospital ward based on ethnographic fieldwork. The initially definition is refined by the introduction of 7 parameters: (i) the degree of distribution of work; (ii) the multiplicity of webs of significance; (iii) the level of required articulation work; (iv) multiplicity and intensity of means of communication; (v) the web of artefacts; (vi) immaterial mechanisms of interaction; (vii) the need for precision and promptness of interpretation. These parameters provide a more detailed conceptual framework and can be applied to characterize the particularity of a given CIS.