A facial expression results from one or more motions or positions of the muscles of the face. They are closely associated with our emotions. Charles Darwin noted in his book The Expression of the Emotions in Man and Animals:

In the mid-20th century most anthropologists believed that facial expressions were entirely learned and could therefore differ among cultures, but studies (eventually with people of the Papua New Guinea highlands who had not been in contact with the outside world) have supported Darwin's belief to a large degree, particularly for expressions of anger, sadness, fear, surprise, disgust, contempt and happiness. Research has also shown that consciously making expressions can induce the corresponding emotion.

Facial expressions are a form of nonverbal communication, and can be voluntary or involuntary. Most people's success rate at reading emotions from facial expression is only a little over 50 percent. Microexpressions, brief flashes of a facial expression, are likely to be involuntary and unconscious, and most people do not learn to read them at all. Recognizing facial expressions uses some of the same brain systems as face recognition.