Facial expressions are considered central in conveying information about one's emotional state. During social encounters, facial expressions of another individual are often automatically imitated by the observer, a process referred to as ‘facial mimicry’. This process is assumed to facilitate prosocial behaviour and is thought to rely on the mirror neuron system, known for its involvement in both observation and execution of motor actions. However, recent studies have revealed mimicry to be a more dynamic process than previously conceptualized, leaving mere perception-action coupling insufficient to explain its behavioural flexibility. In the current review, we describe the consequences of these findings for the theoretical conceptualization of facial mimicry, and present a novel neuroendocrine model for the dynamic modulation of facial mimicry. Our model can guide research on the communicative function of facial expressions and can provide insight into the position of facial mimicry in theoretical models of empathy and social interaction.