This article provides an overview of conversation analytic research that investigates the phenomenon of interlocutors "finishing each other's sentences," termed "collaborative completion, in everyday conversation. The objective is twofold: (1) by reporting on research that examines the formal features and the social actions of collaborative completions, this paper provides a comprehensive overview of both what this practice looks like and what it can achieve in interaction; and (2) in discussing this particular body of work with respect to the larger topic of how language is studied, the author hopes to demonstrate the power of the CA approach to deepen our understanding of the nature of language and how language is used. The paper first reviews the formal features of collaborative completions, namely its syntactic, paralinguistic, and sequential characteristics. Then, the various social actions that can be accomplished with this practice are discussed. Finally, some important themes and suggested directions for future research are mentioned and contextualized within some of the larger objectives of CA research.