In this chapter Wolvin reviews some of the principal research and theory in listening in order to provide a foundation for building listening theory. Recognizing that a great deal of work has been done in the study of listening, he proposes that this work can be characterized from physiological, psychological, sociological, and communicative perspectives which frame an engagement theory of listening. These perspectives can enable listening scholars, teachers, and practitioners to identify more fully the principles underlying their work in this important communication function. Powers (1995) has offered a conceptual model for understanding the intellectual structure of the communication field, suggesting that we can organize our knowledge into tiers: content and form of messages; communicators; levels of communication; and communication contexts. Interestingly, most of the theory that groups in the "communicators" category centers on the communicator as producer/sender of the communication messages.