Despite the longstanding and widespread interest in how people perceive others’ emotions from facial expressions, much of the empirical data comes from a small number of artificially posed stimuli (e.g., the Ekman faces), validated only by high levels of agreement about what emotion they are showing (e.g., labeled as angry, happy, sad, etc.). This ignores a separate—and potentially critical—dimension of facial expressions: whether or not they are perceived as showing genuine emotion. Here, we present evidence that many of the most popular expression stimuli are perceived as not showing genuine emotion. Using new sets of genuine-posed and naturalistic expression stimuli developed in our lab, we find that perceptions of emotion genuineness influence people’s responses in ways that provide new insights into affective processes (e.g., in social anxiety) and sometimes lead to different research conclusions (e.g., in psychopathic traits). Recently, our lab has begun interrogating what physical information in faces causes expressions to be perceived as genuine versus fake. Our findings challenge existing work, and in doing so highlight another emergent issue in the literature: the use of virtual faces as though they were real human ones. Overall, we argue there are significant theoretical and practical benefits to be gained from using stimuli that cover a fuller range of real-world facial behaviour, including expressions that are perceived as showing genuine emotion.