Faces are not simply blank canvases upon which facial expressions write their emotional messages. In fact, facial appearance and facial movement are both important social signalling systems in their own right. We here provide multiple lines of evidence for the notion that the social signals derived from facial appearance on the one hand and facial movement on the other interact in a complex manner, sometimes reinforcing and sometimes contradicting one another. Faces provide information on who a person is. Sex, age, ethnicity, personality and other characteristics that can define a person and the social group the person belongs to can all be derived from the face alone. The present article argues that faces interact with the perception of emotion expressions because this information informs a decoder's expectations regarding an expresser's probable emotional reactions. Facial appearance also interacts more directly with the interpretation of facial movement because some of the features that are used to derive personality or sex information are also features that closely resemble certain emotional expressions, thereby enhancing or diluting the perceived strength of particular expressions.Keywords: emotion; facial expression; facial appearance Facial expressions of emotion have long been of interest to philosophers and psychologists. Darwin's (1872Darwin's ( / 1965 seminal work On the Expression of the Emotions in Man and Animals was a first attempt to systematically understand emotion expression and its meaning. In this book, he proposed a number of explanations as to why certain facial and bodily behaviours communicate certain emotions. In doing so, Darwin had no doubt that the expressive behaviour that he described was part of an underlying emotional state, that is, that emotion expressions have communicative value specifically because they are outward manifestations of an inner state. Darwin assumed clear parallels and antecedents to human emotions in the emotions of animals and our humanoid ancestors, and consequently considered emotion expressions to be universal across human cultures.