In this paper, a discourse modeller for conversational spoken dialogue systems, called GALATEA, is presented. Apart from handling the resolution of ellipses and anaphora, it tracks the “grounding status” of concepts thatare mentioned during the discourse, i.e. information about who said what when. This grounding information also contains concept confidence scores that are derived from the speech recogniser word confidence scores. The discourse model may then be used for concept-level error handling, i.e. grounding of concepts, fragmentary clarification requests, and detection of erroneous concepts in the model at later stages in the dialogue.