In their cooperative effort, architects depend critically on elaborate coordinative practices and artifacts. The article presents, on the basis of an in-depth study of architectural work, an analysis of these practices and artifacts and shows that they are multilaterally interrelated and form complexes of interrelated practices and artifacts which we have dubbed `ordering systems'. In doing so, the article outlines an approach to investigating and conceiving of such practices. Key words: architectural work, classification, coordinative artifacts, common information spaces, indexation, nomenclatures, notations