To understand how a person is feeling just from hearing his or her voice is not something that is very easy to do. Perhaps it is a nearly impossible task. Yet, there are times when an individual (a police officer, for example) has little else but the heard voice to tell him or her what action the talker is intending to take. While some of the relationships between vocal behaviors and emotions are known or suspected, they are tenuous enough that you cannot expect this chapter to be replete with illustrative cases or with descriptions of systems which would allow you to interpret a person’s mental state from listening to his or her voice. Nonetheless, this area of study is an important one and probably will prove amenable to development over time—that is, as more and more relevant research is completed.