ABSTRACT CSCW seems to have a persistent problem of understanding the nature of “cooperative workp’.~ is paper argues that thii problem is a direct restit of not looking at the dynamic aspects of work–Le. that cooperative work is not one timg, but ditierent things at~ erent times and in different places. Based on Activity~ eory the paper gives a concepturd frame for understanding the dynamics of collaborative work activities, and argues that the design of computer support shotid view cooperative breakdowns not ns a problem but as an important resource in design.~ ese==~ ents are based on empirical studies of hedthcare work and the desi~ of a computer support for planning and schedtimg operations and other activities witim a hospiti.