This article describes how it could be possible for two participants engaged in conversation to jointly produce a single syntactic unit such as a sentence. From an inspection of sentence types that are achieved through such joint production, it was determined that participants have available a single utterance construction format. This format, the compound turn-constructional unit format, may be a component of a socially construed syntax-for-conversation. It can be constituted by a wide range of interactionally relevant features of talk in interaction that reveal an emerging utterance as a multiple component turn-constructional unit. The compound turn-constructional unit format is primarily a resource for turn-taking. It can be used to project the next proper place for speaker change. However, it concomitantly provides the resources needed to complete the utterance-in-progress of another participant, thus allowing for the construction of a single sentence across the talk of two speakers. (Conversation, interaction, recognizable activity)The central task of this report is the characterization of single sentences that are produced across the talk of two (or more) speakers. This can be seen in Example (1), where the recipient of an ongoing turn produces a completion for the not-yet-completed turn.(1) [CDHQ:ll] Marty: Now most machines don't record that slow. So l'd wanna-when l make a tape, -> Josh:be able tuh speed it up.The collaboration of two speakers within what is achieved as a single sentence provides a way to recover features of sentence structure, where those features are not wholly tied to the talk of individual speakers.' Sentence production can be seen here as an interactional achievement? The import of this is that the completion of one speaker's utterance by another participant reveals aspects of an interactionally relevant syntax. Rather than simply describing the "historical" constituents of a complete sentence, the examination of this type of collaboration makes possible the description of features of a sentence-in-progress.