This article is meant to present a specific elaboration of the notion of mediation in relation to the use of artefacts to enhance mathematics teaching and learning: the elaboration offered by the Theory of Semiotic Mediation. In particular, it provides an explicit model--consistent with the activity-actions-operations framework--of the actions which are expected from the teacher in order to make mathematics learning occur through the mediation of an artefact. The teacher's actions are identified by their goals and are related to the motive of the teaching-learning activity.