Human facial expressions are unique in their ability to express emotions and communicate them to others. Basic emotions are expressed similarly across cultures and share features with other mammals, suggesting a common genetic origin of the link between facial expressions and emotions. However, recent studies also show cultural influences and differences. The recognition of emotions from facial expressions and the process of expressing one's emotions facially occur within a complex cerebral network. Due to the complexity of the cerebral processing system, various neurological and psychiatric disorders can significantly disrupt the coupling of facial expressions and emotions. Wearing masks limits our ability to convey and recognize emotions through facial expressions. Facial expressions can not only express "real" emotions but also acted ones, allowing for socially acceptable expressions and conscious faking of emotions. These fakes are often imperfect and may be accompanied by brief facial movements indicating actual emotions (microexpressions). Microexpressions are short-lived and often imperceptible to humans but are ideal for computer-aided analysis. Automatic identification of microexpressions has gained scientific attention and is being tested in security-related areas. This article summarizes the current state of knowledge on facial expressions and emotions.Human facial expressions are unique in their ability to express emotions and communicate them to others. Basic emotions are expressed similarly across cultures and share features with other mammals, suggesting a common genetic origin of the link between facial expressions and emotions. However, recent studies also show cultural influences and differences. The recognition of emotions from facial expressions and the process of expressing one's emotions facially occur within a complex cerebral network. Due to the complexity of the cerebral processing system, various neurological and psychiatric disorders can significantly disrupt the coupling of facial expressions and emotions. Wearing masks limits our ability to convey and recognize emotions through facial expressions. Facial expressions can not only express "real" emotions but also acted ones, allowing for socially acceptable expressions and conscious faking of emotions. These fakes are often imperfect and may be accompanied by brief facial movements indicating actual emotions (microexpressions). Microexpressions are short-lived and often imperceptible to humans but are ideal for computer-aided analysis. Automatic identification of microexpressions has gained scientific attention and is being tested in security-related areas. This article summarizes the current state of knowledge on facial expressions and emotions.