When we want to know what someone is thinking, how they are feeling, or what they might do, the first place we frequently look is to their face. This makes considerable sense because the human face is capable of generating expressions associated with a wide range of affective states; the grimace of pain, the sneer of contempt, the glare of anger, the averted eyes of shame, the wide-eyed look of surprise, the intent stare of interest, the quizzical look of puzzlement, the frozen stare of terror, the radiant smile of joy, the sly grin of mischief, and much more, all emanate from the face. Indeed, it could be argued that the face has the only skeletal muscles of the body that are used, not to move ourselves, but to move others.

Given that the face is an important channel of social communication, among the questions that arise are: What are the major messages that are communicated through this channel, and how are they encoded? Facial actions can clearly be used to communicate information other than an individual's emotional state (see Bavelas, Black, Lemery, & Mullett, 1986; Bavelas & Chovil, chapter 15, this volume; Ekman, 1979; Fridlund, 1994). However, from Darwin (1872/1965) to the present, the main focus of research on facial expression has been on the expression of emotion, and for the bulk of this chapter, we maintain this focus.