Two eyetracking experiments were conducted to investigate how the domain of interpretation for referential expressions is constructed and coordinated during utterance processing. Of particular interest was how the uniqueness requirement for a definite noun phrase (e.g. 'the book') could be satisfied given a particular array of candidate referents. Experiment 1 demonstrated that the conceptual relation expressed by a preposition immediately limits attention to compatible referents and in turn facilitates definite reference to these objects. Experiment 2 showed that domains are further constrained by the judgment of which referents are compatible with an intended action, and that uniqueness can be established by such factors even when several objects compatible with the noun phrase are present in the perceptual field. The results demonstrate that domains of interpretation for referential expressions are constructed and updated dynamically as an utterance unfolds in time, taking both linguistic and nonlinguistic factors into account.