This book is the first corpus-based description of epistemic stance in conversational American English. It argues for epistemic stance as a pragmatic rather than semantic notion: showing commitment to the status of information is an emergent interactive activity, rooted in the interaction between conversational co-participants. The first major part of the book establishes the highly regular and routinized nature of such stance marking in the data. The second part offers a micro-analysis of I think, the prototypical stance marker, in its sequential and activity contexts. Adopting the methodology of conversation analysis and paying serious attention to the manifold prosodic cues attendant in the speakers' utterances, the study offers novel situated interpretations of I think. The author also argues for intonation units as a unit of social interaction and makes observations about the grammaticization patterns of the most frequent epistemic markers, notably the status of I think as a discourse marker.