Two experiments examined the role of common ground in the production and on-line interpretation of wh-questions such as What's above the cow with shoes? Experiment 1 examined unscripted conversation, and found that speakers consistently use wh-questions to inquire about information known only to the addressee. Addressees were sensitive to this tendency, and quickly directed attention toward private entities when interpreting these questions. A second experiment replicated the interpretation findings in a more constrained setting. These results add to previous evidence that the common ground influences initial language processes, and suggests that the strength and polarity of common ground effects may depend on contributions of sentence type as well as the interactivity of the situation.Keywords common ground; eye-tracking; perspective taking; conversation; referential communication; question; comprehension Conversation is a joint activity through which interlocutors exchange information and ideas. According to one influential framework, during conversation, interlocutors develop common ground (Stalnaker, 1978), which includes mutual knowledge that arises from common cultural and community information, information present in a shared environment, and information introduced linguistically (Clark, 1992(Clark, , 1996.Recently, psycholinguists have begun to explore when, in the time course of processing, interlocutors make use of common ground in interpreting definite referring expressions. Most of these studies have used the visual world eye-tracking paradigm (Tanenhaus, SpiveyKnowlton, to examine whether addressees look at referents that are potentially consistent with a referring expression, presented as an instruction, e.g., Put the tape above the apple, when that referent is in their privileged ground (e.g., a display including a Contact Information: Sarah Brown-Schmidt, Beckman Institute, 405 N Mathews Ave, University of Illinois, Urbana-Champaign, Urbana, IL 61801, brownsch@uiuc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. cassette tape, an apple and several other objects visible to both participants, along with a roll of scotch tape that is occluded from the speaker). There is general agreement that the addressee's interpretation is restricted to candidates in common ground; however, studies differ in their conclusions about when common ground constrains referential domains. Some studies suggest that addressees are initially egocentric, considering potential referents of referring expressions, without regard for whether they are in common or privileged...