Winner of the Jake Harwood Outstanding Book Award (2022). What, exactly, is understanding? And how do people create, maintain, and manipulate states of understanding via communication? This book addresses these questions, drawing on interdisciplinary scholarship in cognitive science, communication, psychology, and pragmatics. Rejecting classic descriptions of communication as "sending and receiving messages," this book proposes a novel perspective that depicts communication as a process in which interactants construct, test, and refine mental modes of a joint experience on the basis of the meme states (mental representations) activated by stimuli in social interactions. It explains how this process, when successful, results in interactants' mental models aligning, or becoming entrained—in other words, in creating a state of understanding. This framework is grounded in a set of foundational observations about evolved human cognition that highlight people's intrinsic social orientation, predisposition toward efficiency, and use of predictive interference-making. These principles are also used to explain how codified systems ("codes") emerge in extended or repeated interactions in which people endeavor to create understanding. Integrating and synthesizing research across disciplines, this book offers communication scholars and students a theoretical framework that will transform the way they see understanding, communication, and social connection.