This paper presents a Conceptual Graph (cg) framework to the Generation of Referring Expressions (gre). Employing Conceptual Graphs as the underlying formalism allows a new rigorous, semantically rich, approach to gre: the intended referent is indentied by a combination of facts that can be deduced in its presence but not if it would be absent. Since cgs allow a substantial generalisation of the GRE problem, we show how the resulting formalism can be used by a gre algorithm that refers uniquely to objects in the scene.