In conversation,a person sometimeshasto refer to anobjectthat is not previously known to the other participant. We present a planbased model of how agents collaborate on reference of this sort. In making a reference, an agent uses the most salient attributes of the referent. In understandinga reference,an agentdetermines his confidence in its adequacy as a means of identifying the referent. To collaborate, the agents use judgment, suggestion, and elaboration moves to refashion an inadequate referring expression.