This chapter provides a comprehensive overview of classic and contemporary developments in the social psychological study of language use in social interaction, with a focus on research in conversation analysis. After reviewing traditional social psychological approaches to the study of language—most prominently symbolic interactionism—which conceptualize language as a medium of communication, the chapter lays out the alternative approach of conversation analysis (CA), which treats language as social action and has roots in ethnomethodology and Goffmanian sociology. Next, the chapter describes core features of conversation analytic methodology, followed by a review of CA research at the micro, meso, and macro levels. Finally, the chapter discusses recent quantitative extensions of traditional CA scholarship, which establish statistical relationships between interactional practices and a range of social contexts and outcomes.