We address a problem examined by sociologists of `Big Science': the co-ordination of individuals on large-scale projects - in this case, industrial technology projects. We consider co-ordination to be a problem of social order which can be addressed through ethnomethodology's understanding of accountable action. We propose that the technology producers studied attend to the problem of the co-ordination of their work in the design of their actions and interactions as organizationally accountable. We subsequently examine the methodical practices through which they interrelate their actions within an organizational context, and thus organize the co-ordination of their technological work and the production of their technology outcomes.