The methods of ethnography and cognitive psychology are frequently set in opposition to each other. Whilst such a view may be appropriate in de"ning pure, or prototypical, classes of each activity, the value and necessity of such a distinction is broken down when researchers are goal-directed to study complex work domains in order to foster technological change. In this paper, we outline a rapprochement of these methods, which we term cognitive ethnography. The value of qualifying ethnography in this way is to emphasize systematically the differences between ethnography as a radial category and the kinds of legitimate method used to study work practices which are often referred to as ethnographic, but which in practice di!er in important ways from prototypical ethnographic studies. Features of cognitive ethnography such as observational specifcity, verifability and purposivenes challenge many of the tenets of a pure ethnographic method, yet they are essential for studies that are undertaken to inform technological change. We illustrate our arguments with reference to a project to develop a tool for supporting design re-use in innovative design environments.