The design of CSCW systems has often had its roots in ethnomethodological understandings of work and investigations of working settings. Increasingly, we are also seeing these ideas applied to critique and inform HCI design more generally. However, the attempt to design from the basis of ethnomethodology is fraught with methodological dangers. In particular, ethnomethodology's overriding concern with the detail of practice poses some serious problems when attempts are made to design around such understandings. In this paper, we discuss the range and application of ethnomethodological investigations of technology in working settings, describe how ethnomethodologically-affiliated work has approached system design and discuss ways that ethnomethodology can move from design critique to design practice: the advent of technomethodology.