Shaping shared workspace is a key issue in human organisations. In the same way, shaping the environment in terms of the artefacts constituting the agent workspace is a central issue in the engineering of a multiagent system (MAS). In this lecture, we introduce the notions of artefact for MASs and agent workspace, then discuss some cognitive aspects of the relationship between agents and artefacts. Afterward, we sketch the basic elements of a theory of artefacts, and draw some consequences in terms of theory and practice of MAS engineering.