This article describes research investigating the on-line processing of language in unscripted conversational settings. In particular, we focus on the process of formulating and interpreting definite referring expressions. Within this domain we present results of two eye-tracking experiments addressing the problem of how speakers interrogate the referential domain in preparation to speak, how they select an appropriate expression for a given referent, and how addressees interpret these expressions. We aim to demonstrate that it is possible, and indeed fruitful, to examine unscripted, conversational language using modified experimental designs and standard hypothesis testing procedures.